Repeating thump during washing
The sound starts after the tub fills and repeats every few seconds while water is spraying.
Start here: Check for a spray arm hitting a pan, cutting board, utensil, or lower rack item.
Dishwasher noise troubleshooting
Dishwasher Thumping Noise
Direct answer: A dishwasher thumping noise is most often a spray arm striking a tall item, a utensil poking through a rack, or a damaged spray arm wobbling under water pressure. If the sound is a heavy knock from underneath instead of a repeating tap inside the tub, stop and check for a loose pump area or motor problem.
Most likely: Start by figuring out whether the thump happens only during washing, only during draining, or all through the cycle. A repeating thump during wash usually lives in the spray arms or the load, not the drain system.
A light swish is normal. A steady thump, knock, or rhythmic slap is not. The fastest way to solve this is to pin down where the sound lives and when it starts, then check the easy physical causes before you pull the machine apart.
Don’t start with: Do not start by buying a dishwasher pump. Most thumping complaints turn out to be something in the tub getting hit over and over.
If the noise changes when you rearrange dishes,look hard at the spray arms, tall items, and utensils sticking through the rack.
If the noise comes from low in the machine during drain-out,shift your attention to the drain path or pump area instead of the spray arms.
Last reviewed: 2026-04-01
What the thumping sounds like and where to start
Fast tapping from inside the tub
It sounds lighter than a motor knock and may change as the racks move or the load shifts.
Start here: Inspect both dishwasher spray arms for cracks, looseness, or debris that makes them wobble.
Heavy knock from underneath
The sound seems lower and duller, and it may be strongest during drain or right after wash action starts.
Start here: Look for standing water, filter blockage, or signs the dishwasher pump area is struggling.
Noise only with a full load
The dishwasher sounds normal empty or lightly loaded but thumps with plates, pans, or utensils packed in.
Start here: Focus on loading interference before assuming a failed internal part.
Most likely causes
1. Dishwasher spray arm hitting dishes or utensils
This is the most common cause of a rhythmic thump. The sound repeats as the spray arm comes back around under water pressure.
Quick check: Spin the upper and lower dishwasher spray arms by hand with the racks loaded the way you normally run them. If either arm touches anything, you found a likely cause.
2. Cracked, warped, or loose dishwasher spray arm
A split or wobbling spray arm can slap water unevenly, clip nearby items, or knock as it rotates.
Quick check: Remove the racks enough to see the arms clearly. Look for a loose hub, a bent arm, or a seam that has opened up.
3. Utensil, rack tine, or small item hanging into the spray path
A spoon, lid, or lightweight container can drop just enough to get hit once each rotation.
Quick check: Check for utensils poking below the silverware basket, small lids flipped loose, or a rack tine that lets items sag into the arm path.
4. Dishwasher pump or drain area making a lower knock
If the sound is not coming from the spray pattern inside the tub, a blocked filter, hard debris, or a failing pump can create a heavier thump or knock.
Quick check: Listen for whether the noise happens during drain-out, and inspect the dishwasher filter area for debris or standing water.
Step-by-step fix
Step 1: Pin down when the thump happens
You need to separate a wash-side thump from a drain-side knock before touching parts. They sound similar from across the kitchen, but they are not the same problem.
- Run a short cycle and stay nearby for the first few minutes.
- Listen for whether the thump starts after filling, during active spraying, during drain-out, or all the way through.
- Open the door briefly when the thump is happening if your dishwasher allows it safely. A wash-side thump usually stops immediately when the spray arms stop.
- Note whether the noise is a light repeating tap from inside the tub or a heavier knock from low underneath.
Next move: If you can tie the sound to the wash portion, go straight to the spray arm and loading checks. If it clearly happens during drain, skip ahead mentally to the filter and pump area. If you cannot tell when it happens, treat the tub-side checks as the first move anyway because they are safer and far more common.
What to conclude: A repeating thump during wash usually points to spray arm interference or a damaged spray arm. A lower knock during drain points more toward debris or trouble in the pump area.
Stop if:
- You smell burning insulation or hot plastic.
- Water is leaking onto the floor.
- The noise is violent enough that the dishwasher is shifting in the cabinet.
Step 2: Check the load and anything the spray arms can hit
This is the highest-odds fix and the least destructive one. One tall tray, pan handle, or spoon can make a dishwasher sound much worse than it is.
- Turn power to the dishwasher off at the controls before reaching inside.
- Pull out the lower rack and look for baking sheets, pot handles, cutting boards, or large plates sticking into the center spray path.
- Check the silverware basket for long utensils hanging low enough to catch the lower dishwasher spray arm.
- Look at the upper rack too. A tall cup, bottle, or hanging utensil can interfere with the upper dishwasher spray arm.
- Rearrange anything close to the spray path and make sure lightweight items are secured so they cannot flop down mid-cycle.
Next move: If the thumping disappears after reloading, the machine is likely fine. Keep using it, just load with more clearance around the spray arms. If the noise stays with an empty or carefully loaded rack, inspect the spray arms themselves next.
What to conclude: If loading changes the sound, you are dealing with interference inside the tub, not a motor or control problem.
Step 3: Inspect both dishwasher spray arms for wobble, cracks, and blockage
A damaged spray arm can thump even with a perfect load. Split seams, clogged jets, or a loose center mount make the arm rotate badly and slap water unevenly.
- With the dishwasher empty, spin the lower dishwasher spray arm by hand. It should turn freely without scraping or dropping.
- Check the lower dishwasher spray arm for cracks, separated seams, or a loose center connection.
- Inspect the upper dishwasher spray arm the same way, including its mount under the rack or feed tube area.
- Look for food debris in the spray holes that could throw the arm off balance. Rinse with warm water and clear debris gently with a toothpick or soft pick, not a drill bit or metal screw.
- Make sure the spray arm is seated correctly and not partly popped off its mount.
Next move: If you find a loose or damaged spray arm and correct the fit or replace that arm, a rhythmic wash thump usually goes away. If both spray arms look solid and clear, move to the filter and pump-area check.
Step 4: Check the dishwasher filter area and drain side for debris
A lower knock or thump can come from hard debris in the sump area or a pump struggling against blockage. This is also where a wash-side complaint sometimes turns out to be a drain-side problem.
- Disconnect power to the dishwasher before removing the filter.
- Remove the dishwasher filter and rinse it with warm water. Use mild dish soap if greasy, and a soft brush only if needed.
- Look into the filter well for labels, glass, bone fragments, fruit pits, or other hard debris.
- If there is standing water, note that separately because a drain problem may be part of the noise complaint.
- Reinstall the dishwasher filter correctly and make sure it locks or seats fully before testing again.
Next move: If the thump is gone after cleaning out debris and reseating the filter, you likely had something getting kicked around in the sump area. If the noise is still a heavy lower knock, the pump area may need closer inspection or service.
Step 5: Test one more time, then decide between a spray arm fix and a pro pump inspection
By now you should know whether the thump lives in the tub or lower in the machine. That keeps you from buying the wrong part.
- Run a short rinse cycle with the dishwasher empty except for the racks.
- If the noise is gone empty but returns loaded, correct the loading pattern and watch for items dropping into the spray path.
- If the noise stays empty and you already found a cracked or loose dishwasher spray arm, replace that spray arm.
- If the noise stays empty, comes from low in the machine, and the filter area is clean, stop short of blind part-buying and have the dishwasher pump area inspected.
- If the sound is actually a harsher grind instead of a thump, switch to the dishwasher grinding noise problem page for a better match.
A good result: If the empty-cycle test is quiet, you solved it with loading or a spray arm correction. If a confirmed spray arm replacement fixes it, verify wash coverage and move on.
If not: If the dishwasher still makes a heavy lower thump empty with a clean filter area, the next move is service-level pump diagnosis rather than guessing.
What to conclude: A quiet empty cycle points to interference in the tub. A persistent lower knock empty points to an internal mechanical issue that is not worth guessing at from the outside.
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FAQ
Is a thumping dishwasher always a bad pump?
No. Most thumping complaints are simpler than that. A spray arm hitting a dish or a loose item in the rack is much more common than a failed dishwasher pump.
Why does my dishwasher only thump when it is full?
That usually points to loading interference. A tall plate, pan handle, bottle, or hanging utensil can sit just low enough to get hit once each rotation.
Can a cracked spray arm make a knocking sound?
Yes. A cracked or warped dishwasher spray arm can wobble, slap water unevenly, or clip nearby items. That often sounds like a repeating thump during the wash portion.
Should I keep running the dishwasher to see if the noise clears up?
No. That is a common wrong move. Repeated testing can chew up a damaged spray arm, scatter debris into the pump area, or let a loose item melt or break.
What if the noise is more like grinding than thumping?
That is a different clue. A harsher grind points away from simple spray arm interference and more toward debris or a mechanical problem. Use the dishwasher grinding noise page if that matches better.
Can the filter cause a thumping noise?
Indirectly, yes. If the dishwasher filter is damaged, loose, or letting hard debris reach the sump area, you can hear knocking or thumping from low in the machine.