A dishwasher making a knocking noise can be concerning, particularly when the sound is loud, repetitive, or suddenly appears after years of relatively quiet operation. However, a knocking sound does not automatically mean that the dishwasher has a serious mechanical fault.
Many dishwashers naturally produce different sounds during a wash cycle. Water enters through the inlet valve, pumps circulate water, spray arms rotate, dishes are exposed to strong water jets, and the drain pump removes wastewater. These processes can create humming, swishing, whooshing, clicking, and occasional gurgling sounds.
A repetitive knocking or thumping noise, however, deserves closer attention. In many cases, the cause is surprisingly simple: a spray arm is striking a dish, utensil, pan, or other object because the dishwasher has been loaded incorrectly. A loose or damaged spray arm, moving dishes, an obstructed pump, loose installation components, plumbing movement, or a worn pump can also produce knocking sounds.
The timing of the noise is particularly important. A knock that occurs every few seconds during the wash phase has a different likely cause from a bang that occurs when the dishwasher fills with water or a mechanical knocking sound that continues while the machine is empty.
This guide explains the most common causes of dishwasher knocking noises, how to identify the source, what you can safely check yourself, when a repair may be necessary, and how to prevent the problem from returning.
Is a Knocking Noise From a Dishwasher Normal?
Some dishwasher noises are completely normal.
During the wash phase, pressurized water is sprayed against the dishes and the interior of the tub. The rotating spray arms can produce a rhythmic swishing or whooshing sound. Pumps and motors can produce a steady hum, while the drain system can produce a brief gurgling sound as water is removed.
The sound level also depends on the dishwasher’s construction and installation. Insulation, cabinet placement, flooring, tub materials, and the appliance’s location can all influence how much operating noise reaches the kitchen.
A knocking noise is different when it is clearly an impact sound.
For example, a repetitive knock-knock-knock every few seconds during washing is often caused by a rotating spray arm striking something inside the dishwasher. If the sound occurs only when dishes are loaded and disappears when the dishwasher is empty, the load itself becomes an important suspect.
On the other hand, a knocking noise that remains when the dishwasher is completely empty may indicate a problem involving a pump, spray arm, rack, mounting system, plumbing connection, or another mechanical component.
The goal is not to eliminate every sound a dishwasher makes. Instead, the goal is to determine whether the sound is consistent with normal operation or whether it represents an abnormal impact or mechanical noise.
How to Identify the Type of Knocking Noise
Before removing components or calling for service, pay attention to exactly when the noise occurs.
Ask yourself:
- Does the noise happen during washing?
- Does it occur when the dishwasher fills?
- Does it happen during draining?
- Does it happen only with dishes inside?
- Does it happen when the dishwasher is empty?
- Is the knocking rhythmic?
- Is it random?
- Is it loud or relatively soft?
- Does the dishwasher shake at the same time?
- Does the noise come from inside the tub?
- Does it sound like it comes from underneath or behind the appliance?
These details can narrow the possible causes considerably.
Knocking every few seconds during washing
This strongly suggests that something is interfering with a rotating spray arm.
Knocking only when dishes are loaded
Loose dishes, utensils, pans, lids, or plastic containers are likely possibilities.
Knocking when the dishwasher fills
Water-supply movement or water hammer may be involved.
Knocking during draining
The drain pump, drain area, or a foreign object may need inspection.
Knocking while empty
Mechanical, installation, or plumbing-related causes become more likely.
Knocking accompanied by severe vibration
Leveling, mounting, cabinet contact, or a mechanical problem should be investigated.
1. The Spray Arm Is Hitting a Dish
The most common reason for a rhythmic dishwasher knocking noise is a spray arm hitting an object inside the dishwasher.
Spray arms rotate during the wash cycle as water pressure passes through their openings. They require enough clearance to rotate without contacting dishes, cookware, utensils, racks, or other components.
If a plate is too tall, a pan handle extends too far, or a utensil is positioned incorrectly, the spray arm may strike it every time it rotates to that position.
The result is a repetitive knocking or thumping sound.
This problem can occur even if the dishwasher appears to be properly loaded.
How to check
Stop the dishwasher and open the door.
Inspect the lower rack first. Look for:
- Tall plates
- Large bowls
- Pan handles
- Baking trays
- Cutting boards
- Long utensils
- Serving spoons
- Cooking tools
Then rotate the lower spray arm by hand.
It should be able to move without striking anything.
If you feel or hear the spray arm hitting an item, rearrange the load.
After repositioning the dishes, rotate the spray arm again before restarting the dishwasher.
2. The Middle or Upper Spray Arm Is Being Blocked
The lower spray arm is not the only component that can create knocking.
Many modern dishwashers have a spray arm underneath the upper rack or integrated into the rack itself. A tall glass, plate, pan, or utensil can interfere with this spray arm.
Adjustable upper racks can make this more complicated because changing the rack height changes the available clearance.
If the knocking seems to come from the middle or upper portion of the dishwasher, inspect the upper rack carefully.
Make sure tall items are not positioned directly underneath the spray arm.
Spin or move the accessible spray arm manually according to the appliance’s instructions.
If the arm cannot rotate freely, rearrange the dishes.
3. The Dishwasher Was Loaded Incorrectly
Dishwasher loading is one of the most important factors affecting noise.
Dishes should be positioned securely between rack tines. They should not be balanced loosely or placed at angles that allow them to move significantly under the pressure of the water jets.
Large items can obstruct spray arms, while lightweight items can move around.
Improper loading can cause:
- Knocking
- Rattling
- Clattering
- Scraping
- Poor cleaning
- Blocked spray arms
- Broken glassware
- Water-flow problems
A dishwasher should not be packed simply to maximize the number of dishes in one cycle.
The objective is to achieve a load that is both stable and accessible to the water jets.
4. Large Pots and Pans Can Cause Knocking
Large cookware is a frequent source of spray-arm interference.
A frying pan may have a handle that extends toward the center of the dishwasher. A roasting tray may sit at an angle. A saucepan can lean upward and block a spray arm.
Because spray arms rotate continuously, the resulting noise may be extremely regular.
You may hear a knock every few seconds throughout the washing portion of the cycle.
If the noise started after you loaded a particularly large pan, inspect that item first.
Move it to another location and manually rotate the spray arm.
If the noise disappears, you have found the cause.
5. Loose Cutlery Can Knock Against the Rack
Knocking noises can also come from forks, spoons, knives, tongs, whisks, and cooking utensils.
Water pressure can cause unsecured cutlery to move.
A long spoon may fall sideways and strike the rack. A lightweight utensil can move into the path of a spray arm. Two metal objects can repeatedly strike one another.
Long utensils require particular care because they can extend into areas where they do not belong.
Keep cutlery separated according to the dishwasher’s rack design, and make sure longer objects cannot interfere with spray-arm rotation.
6. Lightweight Plastic Items Are Moving
Plastic containers and lids are much lighter than ceramic plates or metal cookware.
Strong water jets can move unsecured plastic objects during the wash cycle.
A lid may flip over, a container may slide across the rack, or a lightweight cup may vibrate against another item.
The resulting sound may be described as knocking, tapping, clattering, or rattling.
If the dishwasher is quiet with ceramic dishes but noisy when plastic containers are included, inspect how those lightweight items are positioned.
Use the rack area intended for plastic items and secure them so that water pressure cannot easily move them.
7. Dishes Are Knocking Against Each Other
Dishwasher water jets can cause dishes to move if they are positioned too closely together or are not properly supported by the rack.
Two plates may repeatedly contact each other.
A glass may vibrate against a neighboring cup.
A bowl may move against a plate.
This can create a surprising amount of noise inside the metal dishwasher tub.
If the dishwasher is overloaded, this becomes more likely.
Separate dishes where possible and make sure each item is properly supported by the rack structure.
8. The Dishwasher Is Underloaded
Overloading is a common problem, but underloading can sometimes contribute to noise too.
When only a few lightweight items are placed in the dishwasher, they may have more freedom to move around under strong water jets.
Some dishwasher designs may also produce more noticeable water noise when the load is very light because water can strike exposed portions of the tub.
If your dishwasher is exceptionally lightly loaded and the noise appears to come from dishes moving around, distribute the items more securely.
However, do not add dishes simply to make a noise disappear if doing so would violate the manufacturer’s loading recommendations.
9. The Spray Arm Is Loose
If the dishwasher continues knocking after you have completely rearranged the load, inspect the spray arm.
A spray arm should be properly secured according to the dishwasher’s design.
A loose spray arm may wobble during operation.
That movement can cause it to contact the rack, tub, dishes, or other components.
With the dishwasher turned off, gently inspect the spray arm for excessive movement.
Do not force it or apply excessive pressure.
Different dishwasher models use different attachment systems, so follow the instructions for the particular appliance.
10. The Spray Arm Is Damaged
A cracked, warped, or broken spray arm can cause unusual movement.
Inspect the arm for:
- Cracks
- Splits
- Broken mounting points
- Warping
- Loose pieces
- Missing sections
- Severe mineral deposits
A damaged spray arm may not rotate correctly.
Even if the dishwasher still appears to clean reasonably well, a damaged arm can eventually create additional problems.
Replacing a damaged spray arm with the correct model-specific part is generally preferable to attempting to glue or permanently modify it.
11. The Spray Arm Has Mineral Deposits
Hard water can gradually leave mineral deposits on dishwasher components.
The severity depends on the mineral content of the local water supply.
Areas with hard water in the United States, Canada, and the United Kingdom can experience greater accumulation of calcium and magnesium deposits.
Mineral deposits may appear as:
- White crust
- Chalky residue
- Cloudy buildup
- Deposits around spray holes
Heavy buildup can interfere with water flow.
If you see substantial mineral accumulation, clean the spray arm using the manufacturer’s recommended procedure.
Do not automatically use strong acids or household descaling products without confirming that they are suitable for the dishwasher.
12. The Spray Arm Holes Are Blocked
Food particles and mineral deposits can sometimes obstruct spray-arm openings.
When the water flow is restricted, spray performance can change.
A partially blocked spray arm may also behave differently during rotation.
Inspect the openings for visible debris.
If cleaning is necessary, use the procedure recommended for your dishwasher.
Avoid enlarging the holes with sharp tools. Changing the size or shape of spray openings can alter the water pressure and spray pattern.
13. A Foreign Object Is Near the Pump
A dishwasher pump operates under water and can encounter debris.
Small hard objects can enter the sump area, including:
- Broken glass
- Food bones
- Fruit pits
- Small pieces of plastic
- Toothpicks
- Packaging fragments
- Broken dish pieces
A foreign object near a pump can produce unusual mechanical noise.
If the knocking seems to originate from the bottom of the dishwasher rather than the racks or spray arms, inspect the accessible filter and sump area according to the manufacturer’s instructions.
Be extremely careful with glass.
Never reach blindly into an area where broken glass may be present.
14. The Pump Impeller May Be Obstructed
The circulation or drain pump may contain a rotating impeller.
If debris becomes trapped around the impeller, the component may produce unusual sounds.
Some dishwashers provide user-accessible pump areas beneath the filter, while others do not.
If your manufacturer’s instructions specifically provide a procedure for checking the pump, follow that procedure.
Before accessing internal components, disconnect the dishwasher from its electrical supply as instructed.
If the pump area is not designed for user servicing, contact a qualified technician.
15. The Filter Is Dirty
A dirty dishwasher filter may not directly cause knocking, but it can contribute to circulation and pump problems.
The filter is designed to capture food particles and other debris.
Over time, a heavily contaminated filter can restrict water flow and reduce dishwasher performance.
Routine filter cleaning is therefore important.
How often you should clean the filter depends on usage and the type of dishes being washed.
Homes that frequently wash heavily soiled cookware may need more frequent filter maintenance.
Always reinstall the filter correctly.
A filter that is improperly installed can create additional problems.
16. The Dishwasher Is Not Level
A dishwasher that is not level may vibrate more than expected.
Pumps and motors naturally create some movement. Proper installation helps prevent that movement from being transmitted excessively into the surrounding cabinetry.
If the appliance is not level, normal operation can become noticeably louder.
Check whether the dishwasher appears to sit evenly.
A spirit level can be used to assess the appliance, but the exact leveling procedure varies by model.
If the dishwasher is built into cabinetry, do not pull it out unnecessarily without knowing how it is mounted and supported.
17. The Dishwasher Is Not Properly Secured
Built-in dishwashers are normally secured to surrounding cabinetry or another approved structure.
If mounting hardware is loose, the appliance can move during operation.
The result may be:
- Knocking
- Vibrating
- Rattling
- Cabinet movement
- Door movement
A dishwasher that shifts noticeably when operating should be inspected.
Do not remove mounting brackets without understanding the installation system.
If you suspect an installation problem, professional service may be preferable.
18. The Toe-Kick Panel Is Loose
A loose lower access panel can amplify vibration.
The panel may vibrate against the dishwasher frame or surrounding cabinetry and create a knocking or tapping noise.
This can be particularly confusing because the noise may appear to originate from underneath the dishwasher.
Inspect the accessible toe-kick or lower panel.
Look for loose screws, clips, or mounting points.
Only use appropriate replacement hardware.
Do not install screws where they could contact electrical wiring, plumbing, or moving components.
19. The Dishwasher Is Touching the Cabinet
A dishwasher is installed within a relatively tight opening.
If the appliance is incorrectly positioned, vibration can cause it to contact surrounding cabinetry.
Normal pump or motor vibration may then become an audible knock.
This is especially likely if:
- The noise is strongest at certain speeds.
- The dishwasher shakes slightly.
- The cabinets vibrate.
- The noise changes when the door is opened.
- The problem began after installation or renovation.
The dishwasher should be properly positioned, leveled, and secured according to its installation instructions.
20. Water Hammer Can Cause a Knocking Sound
Water hammer is another important possibility.
When flowing water is stopped rapidly, pressure changes can travel through plumbing.
The resulting sound may resemble a bang or knock.
If your dishwasher makes a knocking sound exactly when the water valve opens or closes, the plumbing system should be considered.
Water hammer may be particularly noticeable in kitchens where pipes are not adequately supported.
The noise may appear to come from inside the dishwasher even though the actual sound is traveling through the water supply system.
If you suspect water hammer, a qualified plumber can inspect the supply system and determine whether additional pipe support or a suitable water-hammer control device is necessary.
21. The Water Inlet Valve May Be Noisy
The inlet valve controls the flow of water into the dishwasher.
Some sound from the valve is normal.
However, unusual vibration or a loud impact when the valve operates can indicate a valve or plumbing-related problem.
Pay attention to the timing.
If the knocking occurs precisely when the dishwasher begins filling, the inlet system becomes more likely.
If the noise occurs throughout the wash period, the spray system is more likely.
This distinction can prevent unnecessary replacement of expensive components.
22. The Drain Hose May Be Moving
The drain system can also produce noise.
When water is pumped out, the drain hose may experience movement.
If a hose is poorly positioned or able to contact the cabinet or another hard surface, the resulting vibration can produce a knocking sound.
Inspect accessible portions of the drain connection for obvious movement or contact.
Do not alter the drain configuration unless you understand the dishwasher’s installation requirements.
Incorrect drain installation can cause drainage and sanitation problems in addition to noise.
23. The Wash Pump May Be Worn
A dishwasher’s circulation pump operates repeatedly during its life.
Mechanical components can eventually wear.
A worn pump may produce:
- Knocking
- Grinding
- Buzzing
- Rattling
- Humming
- Excessive vibration
Pump-related noise is more concerning when it occurs with the dishwasher empty.
Other symptoms may include poor cleaning performance, weak water circulation, or changes in the sound of the pump over time.
If a dishwasher that was previously quiet develops a persistent mechanical knocking sound, professional diagnosis is appropriate.
24. The Drain Pump May Be Damaged
The drain pump can also become noisy.
A foreign object, worn component, or damaged impeller can cause unusual sounds during the drain phase.
If the knocking occurs only when the dishwasher is removing water, pay particular attention to the drain pump.
You may also notice:
- Slow drainage
- Standing water
- Gurgling
- Grinding
- Intermittent draining
- Unusual vibration
Do not repeatedly operate a dishwasher with an obviously damaged pump.
25. The Dishwasher Has Been Sitting Unused for a Long Time
Dishwashers that have been unused for an extended period can sometimes produce unusual pump sounds when restarted.
Some pump seals and components may behave differently after prolonged inactivity.
If the noise disappears after normal operation and there are no other symptoms, it may not indicate a permanent failure.
However, if the noise persists or becomes louder, the appliance should be inspected.
Never assume that a loud mechanical sound is normal simply because the dishwasher has been unused.
26. A New Dishwasher May Sound Different
New dishwashers can sound very different from older machines.
Modern appliances often use different pump designs, filtration systems, insulation materials, and motor technologies.
A homeowner who replaces an older dishwasher may therefore interpret normal operating sounds as unusual.
The owner’s manual is the best reference for identifying model-specific sounds.
Nevertheless, a distinct repetitive knocking or impact sound should still be investigated, especially if it is not described as normal operation.
How to Fix a Dishwasher Making a Knocking Noise
A systematic approach is safer and more effective than immediately replacing components.
Step 1: Stop the dishwasher
If the noise is unusually loud, stop the cycle.
Do not allow a loose component to continue striking another part of the appliance.
Step 2: Open the dishwasher
Look for obvious loading problems.
Check large cookware, tall dishes, utensils, plastic items, and lids.
Step 3: Rotate the spray arms
With the dishwasher off, rotate accessible spray arms manually.
They should have sufficient clearance.
Step 4: Rearrange the dishes
Separate items that are touching.
Secure lightweight items.
Move large cookware away from spray-arm paths.
Step 5: Check the racks
Make sure the racks are seated correctly.
Check for damaged wheels, rails, or other obvious problems.
Step 6: Inspect the spray arms
Look for cracks, loose components, mineral deposits, and blocked openings.
Step 7: Clean the filter
If the filter is user-removable, clean it according to the manufacturer’s instructions.
Step 8: Inspect the accessible sump area
Look for obvious debris.
Do not reach blindly into the pump area.
Step 9: Run a controlled test
If appropriate for your model, run the dishwasher without dishes.
Listen carefully.
If the noise disappears, loading is the most likely cause.
If the noise remains, investigate installation, plumbing, spray-arm, or mechanical causes.
Why Does My Dishwasher Knock Only When Washing?
A knocking noise that occurs only during the wash phase strongly suggests that something is being moved or contacted by the circulating water.
The spray arm is the first thing to investigate.
As the arm rotates, it may repeatedly hit a plate, pan, utensil, rack component, or another object.
Water jets can also move lightweight dishes.
If the dishwasher is quiet during filling and draining but knocks during washing, start with the racks and spray arms rather than immediately assuming that the motor has failed.
Why Does My Dishwasher Knock Every Few Seconds?
A regular interval is an important clue.
If the sound occurs approximately every few seconds and continues throughout the wash period, the spray arm may be striking something once during each rotation.
For example, a pan handle might sit directly in the spray-arm path.
Each time the arm reaches the handle, it creates a knock.
This can continue for the entire wash cycle.
Rearranging the load is usually the first solution.
Why Does My Dishwasher Knock When Empty?
A dishwasher that knocks while empty requires more investigation.
Possible causes include:
- Loose spray arm
- Damaged spray arm
- Pump obstruction
- Pump damage
- Rack movement
- Installation vibration
- Cabinet contact
- Water inlet noise
- Drain-pump problems
An empty-cycle test is useful because it removes dishes and utensils from the list of possible causes.
If the dishwasher continues knocking when empty, professional service may be appropriate if basic inspection does not identify the cause.
Why Does My Dishwasher Knock During Draining?
A knocking noise during draining may originate from the drain pump or drain system.
Check the filter and accessible drain area.
Look for obvious debris.
If the dishwasher has standing water and the pump is making a loud mechanical noise, avoid repeatedly running the machine.
A foreign object inside the pump can potentially cause further damage.
Why Does My Dishwasher Knock When Filling?
If the noise occurs during filling, consider the water inlet system and household plumbing.
A sudden stop or change in water flow can produce water hammer.
The inlet valve itself can also make operating sounds.
If the sound is clearly coming from the pipes or cabinet behind the dishwasher, a plumbing professional may be better suited to diagnose it.
Can Hard Water Cause a Knocking Dishwasher?
Hard water is not normally the direct cause of a knocking noise.
However, hard water can contribute to mineral deposits on water-contact components.
Heavy buildup can affect spray-arm openings and water flow.
If your dishwasher has visible chalky deposits, regular maintenance and appropriate descaling may help maintain water circulation.
Where a dishwasher has a built-in softening system, configure it according to local water hardness and the manufacturer’s instructions.
Can a Dirty Filter Cause Knocking?
A dirty filter is not the most common direct cause of knocking.
However, accumulated food particles and debris can affect water circulation and may contribute to pump problems.
Cleaning the filter is therefore a sensible part of troubleshooting.
If cleaning the filter does not change the noise, do not assume that the filter was the root cause.
Can Overloading Cause a Knocking Sound?
Yes.
Overloading can create several opportunities for noise.
Dishes may touch one another, utensils may move, and large cookware may obstruct spray arms.
A tightly packed dishwasher may also clean less effectively because water cannot reach surfaces properly.
Loading the appliance according to its rack design is one of the easiest ways to prevent knocking.
Can Underloading Cause Knocking?
It can.
With very few lightweight items in the dishwasher, some objects may have more freedom to move under the force of water jets.
Some dishwasher designs may also produce more noticeable water sounds when the load is light.
If lightweight dishes are moving, reposition them securely.
How to Prevent Dishwasher Knocking Noises
Preventing the problem is usually easier than diagnosing it later.
Load dishes carefully
Do not allow plates, pans, utensils, or containers to interfere with spray-arm movement.
Rotate spray arms before starting
If you are uncertain about clearance, rotate the accessible spray arm by hand.
Secure lightweight items
Plastic containers and lids should be placed where they cannot easily move.
Avoid excessive loading
Do not force dishes into the racks.
Keep spray arms clean
Inspect the spray arms periodically for debris and mineral buildup.
Clean the filter
Follow the recommended filter-cleaning schedule for your model.
Maintain the dishwasher
Routine maintenance helps preserve proper circulation and drainage.
Keep the appliance level
A properly leveled dishwasher is less likely to transmit excessive vibration.
Secure installation components
Mounting brackets, leveling supports, panels, and insulation should remain properly positioned.
Address plumbing noises
If the dishwasher causes pipes to bang when filling, investigate the plumbing rather than assuming that the appliance itself is defective.
Dishwasher Knocking Noise: Quick Diagnostic Table
| When the knocking occurs | Likely causes |
|---|---|
| Every few seconds during washing | Spray arm hitting an object |
| Only when dishes are loaded | Dishes, utensils, pans, or plastic items moving |
| Only with large cookware | Pan or tray interfering with spray arm |
| During filling | Water hammer or inlet system |
| During draining | Drain pump or debris |
| Even when empty | Pump, spray arm, installation, or plumbing |
| When the dishwasher vibrates | Leveling or mounting |
| After installation | Installation or plumbing issue |
| After loading plastic items | Lightweight objects moving |
| Sudden new mechanical noise | Debris, loose component, or worn part |
| Loud grinding plus knocking | Pump or foreign object |
| Knocking with cabinet vibration | Appliance contact or mounting issue |
When Is a Dishwasher Knocking Noise Serious?
Not every knocking noise requires immediate professional repair.
A light rhythmic knock caused by a plate touching a spray arm is usually a loading problem.
However, certain symptoms should not be ignored.
Stop using the dishwasher and investigate if you notice:
- Severe or violent banging
- Strong vibration
- Burning smell
- Smoke
- Water leaking underneath the appliance
- Electrical problems
- Repeated circuit-breaker trips
- Grinding from the pump
- Metallic objects striking continuously
- A damaged spray arm
- A loose mechanical component
- Sudden deterioration in cleaning performance
- Standing water combined with loud pump noise
If the dishwasher has electrical or internal mechanical problems, professional service is safer than attempting an unfamiliar repair.
When Should You Call a Dishwasher Repair Technician?
Professional diagnosis is recommended when the basic troubleshooting steps do not solve the problem.
Call a qualified technician if:
- The dishwasher knocks while completely empty.
- The noise is loud and mechanical.
- The pump appears to be the source.
- A spray arm is damaged or cannot be secured.
- There is significant vibration.
- The dishwasher moves within its cabinet.
- Water is leaking.
- The noise appears to come from internal electrical components.
- A foreign object may be trapped in an inaccessible pump area.
- Plumbing water hammer is suspected and cannot be resolved through basic checks.
- The noise continues or becomes progressively worse.
- The appliance is still covered by a manufacturer’s or retailer’s warranty.
Do not dismantle the appliance unnecessarily, particularly while it is connected to electricity or water.
Should You Keep Running a Dishwasher That Is Knocking?
That depends on the cause.
If the sound was caused by a spoon touching the rack and you have corrected the loading issue, there is generally no reason to treat it as a mechanical failure.
If the dishwasher is making a loud mechanical knocking noise even when empty, continuing to run it repeatedly may not be wise.
The same applies if you notice leaking, severe vibration, grinding, burning smells, or electrical symptoms.
A small problem can sometimes become a much larger repair if a damaged mechanical component continues operating.
Is a Knocking Dishwasher Dangerous?
A simple loading-related knock is usually not dangerous.
However, the noise itself does not provide enough information to guarantee that the appliance is safe.
The surrounding symptoms matter.
A dishwasher that knocks lightly because a pan handle is touching a spray arm is fundamentally different from one that knocks violently while shaking, leaking, or producing a burning smell.
Treat severe or unexplained mechanical noises seriously.
When in doubt, stop the dishwasher and disconnect its power according to the manufacturer’s safety instructions before inspecting accessible components.
Dishwasher Knocking vs. Rattling
Knocking and rattling can have different causes.
A knocking sound is often a repeated impact, such as a spray arm hitting a dish.
A rattling sound may come from loose utensils, lightweight objects, dishes moving, or a mechanical component.
However, people describe appliance noises differently, so the terminology is not enough to diagnose the problem.
The timing and location of the noise are more useful than the exact word used to describe it.
Dishwasher Knocking vs. Grinding
Grinding is generally more concerning than a mild loading-related knock.
A grinding noise from the pump area may indicate a foreign object or mechanical wear.
If you hear both grinding and knocking, particularly when the dishwasher is empty, inspect the accessible filter and pump area according to the manufacturer’s instructions.
If the cause is not obvious, professional diagnosis is recommended.
Dishwasher Knocking vs. Water Hammer
Water hammer is generally associated with the water supply rather than dishes inside the tub.
A plumbing-related knock often happens when water flow changes suddenly.
For example, the noise may occur when the dishwasher begins filling or when the inlet valve closes.
A spray-arm knock, by comparison, normally occurs during the wash phase and tends to repeat at a rhythm associated with spray-arm rotation.
Identifying this distinction can save time and prevent unnecessary appliance repairs.
Frequently Asked Questions
Why is my dishwasher making a knocking noise?
The most common cause is a spray arm hitting a dish, pan, utensil, or other object during rotation. Incorrect loading can also allow dishes and lightweight items to move under water pressure. If the dishwasher knocks while empty, investigate the spray arm, pump, installation, and plumbing.
Why does my dishwasher make a knocking noise every few seconds?
A repetitive knocking sound during washing is commonly associated with the spray arm striking something as it rotates. Rearrange the dishes and manually rotate the spray arm to check for interference.
Why does my dishwasher knock only when washing?
The wash phase is when the circulation pump sends water through the spray arms. If the knock occurs only during this phase, check the spray-arm clearance and dishwasher load first.
Why does my dishwasher knock when it is empty?
An empty dishwasher eliminates dishes and utensils as likely causes. Possible explanations include a loose spray arm, pump obstruction, pump wear, installation vibration, cabinet contact, or plumbing noise.
Can a pan cause my dishwasher to knock?
Yes. Large pots, pans, trays, and baking sheets can extend into the path of a rotating spray arm. Move the cookware and check spray-arm clearance before running another cycle.
Can a loose spray arm make a knocking sound?
Yes. A loose or damaged spray arm can wobble during rotation and strike the rack, tub, or another component.
How do I know if the spray arm is hitting a dish?
Turn off the dishwasher and manually rotate the spray arm. If it contacts a dish, pan, utensil, or rack component, rearrange the load until the arm rotates freely.
Should the dishwasher spray arm spin freely?
The accessible spray arm should generally have enough freedom to rotate without being blocked by dishes or the rack. Exact movement varies by design, so follow your model’s instructions.
Can a dirty dishwasher filter cause knocking?
A dirty filter is not usually the direct cause of knocking, but accumulated debris can affect circulation and pump operation. Cleaning the filter is a useful maintenance step during troubleshooting.
Can hard water cause a dishwasher to knock?
Hard water is not normally the direct cause. However, mineral deposits can accumulate on spray arms and other water-contact components, potentially affecting water flow. Significant buildup should be addressed using the manufacturer’s recommended maintenance procedure.
Why does my dishwasher knock when draining?
The drain pump or drain area may be involved. Check the accessible filter and sump area for debris according to the manufacturer’s instructions. Persistent mechanical noise during draining may require professional diagnosis.
Why does my dishwasher knock when filling?
If the noise happens when water begins or stops flowing, water hammer or the water inlet system may be responsible. If the sound seems to come from the plumbing, have the water supply system inspected.
Can an unlevel dishwasher cause knocking?
Yes. An improperly leveled dishwasher can transmit vibration into the floor or cabinets, potentially creating knocking or rattling sounds.
Can loose cabinets make a dishwasher sound like it is knocking?
Yes. Dishwasher vibration can be transferred to cabinetry. A loose toe-kick panel, mounting component, or surrounding cabinet can amplify normal operating vibration.
Why did my dishwasher suddenly start knocking?
A sudden change may result from a newly damaged spray arm, an object entering the pump area, a loose component, a change in loading habits, installation movement, or mechanical wear.
Why does my dishwasher knock only when I put plastic dishes inside?
Lightweight plastic items can move under strong water jets. Secure them in the appropriate rack position and make sure they cannot contact spray arms or other dishes.
Can overloading a dishwasher cause knocking?
Yes. Overloading can cause dishes to contact each other and can interfere with spray-arm rotation. It can also reduce cleaning performance.
Can an underloaded dishwasher make knocking sounds?
Yes. Lightweight objects in a very small load can move more freely under water pressure. Secure the items appropriately rather than assuming that the appliance has a mechanical fault.
Is a rhythmic knocking dishwasher dangerous?
Not necessarily. A rhythmic knock caused by a spray arm hitting a dish is usually a loading issue. However, severe banging, electrical smells, leaking, violent vibration, or mechanical grinding should be treated as warning signs.
Should I replace my dishwasher because it is knocking?
Usually not without determining the cause. Many knocking noises are caused by loading, spray-arm clearance, installation, or minor maintenance issues. A professional diagnosis can determine whether a repair or replacement makes more sense.
How can I stop my dishwasher from knocking?
Start by rearranging the dishes, checking spray-arm clearance, securing lightweight items, inspecting the racks, and cleaning the filter. If the noise continues when the dishwasher is empty, investigate the pump, installation, and plumbing.
How often should I clean my dishwasher filter?
Follow the cleaning frequency specified for your model. Households that frequently wash heavily soiled dishes may need to clean the filter more often. Regular inspection is useful because food particles and debris can accumulate over time.
Can a broken glass cause dishwasher knocking?
Yes. Broken glass or another hard object can potentially enter the sump or pump area and produce unusual mechanical sounds. Handle suspected glass carefully and do not reach blindly into the pump area.
Can dishwasher knocking damage the appliance?
A minor loading-related knock is unlikely to cause major damage immediately. However, repeatedly operating a dishwasher with a loose mechanical component, obstructed pump, or damaged spray arm can potentially lead to further problems.
Final Thoughts
A dishwasher making a knocking noise is often easier to diagnose than it initially appears.
The first thing to check is the dishwasher load. Large plates, pans, baking trays, utensils, plastic containers, and improperly positioned dishes can interfere with spray-arm movement or move under the force of circulating water. A repetitive knock every few seconds during washing is particularly suggestive of a spray arm contacting an object.
If rearranging the dishes does not solve the problem, check the spray arms themselves. Make sure they can rotate freely and look for cracks, loose attachments, blocked openings, or heavy mineral deposits.
The next step is to investigate the filter and accessible sump area for debris. Broken glass, food fragments, plastic pieces, and other foreign objects can sometimes reach areas near the pump and produce abnormal mechanical sounds.
If the dishwasher knocks while empty, the diagnosis becomes more important. A loose spray arm, pump problem, installation issue, cabinet contact, water inlet problem, drain pump, or plumbing-related water hammer could be responsible.
The timing of the noise is one of your most valuable clues. Knocking during washing often points toward the spray system or dishwasher load. Noise during filling may point toward the inlet system or plumbing. Noise during draining may indicate the drain pump or debris. Noise that continues regardless of the cycle or occurs with an empty dishwasher deserves greater attention.
Dishwashers in the UK, USA, and Canada operate on broadly similar principles, but individual models differ significantly in rack design, spray-arm configuration, pump construction, installation requirements, water-softening systems, and service procedures. Therefore, model-specific instructions should always take priority over generic troubleshooting advice.
Most importantly, do not ignore a severe or progressively worsening noise. If the dishwasher is violently vibrating, leaking, producing a burning smell, repeatedly tripping a circuit breaker, grinding loudly, or knocking even when empty, stop the appliance and arrange an appropriate inspection.
In many cases, however, the solution is simple: load the dishes correctly, give the spray arms enough clearance, secure lightweight items, and keep the dishwasher’s filter and water system properly maintained.
