Dishwasher Noises: Grinding, Humming, Rattling and Thumping

Grinding — stop the cycle

A gritty, metallic grind means something hard is in the pump or chopper area: broken glass, a fruit pit, a bone fragment, or a piece of cutlery that fell through the basket. Continuing the cycle scores the impeller and can destroy the pump seal.

Cancel, let it drain, and check the filter and the sump beneath it. Wear a glove — glass is the usual find. If you cannot see the object and the noise persists, the debris is past the filter and needs the sump opened.

Humming with no drainage

A steady electrical hum during the drain phase with no water leaving the machine means the drain pump is energized but the impeller cannot turn. Usually that is debris; occasionally it is a seized motor.

Clear the filter and sump first. If it hums and drains normally afterwards, you found it.

Thumping and knocking

A rhythmic thump that matches the spray arm's rotation is the arm striking a dish, a pan handle or an overhanging item. Open the door mid-cycle, spin both arms by hand, and reposition whatever they catch on. It is harmless but it also means part of your load is not being sprayed.

A single loud knock when water starts or stops is water hammer in the household plumbing, not a dishwasher fault. An arrestor on the supply line fixes it.

Rattling, buzzing and squealing

Rattling is usually light items shifting under spray, loose rack tines, or a worn rack roller. Buzzing at fill time is the inlet valve, which is normal in moderation but a loud buzz can signal a failing valve or low supply pressure.

A squeal or high whine points at worn bearings in the wash pump motor. That one does not get better and warrants a technician.

• Grinding — hard debris in pump; stop immediately.
• Humming, no drain — jammed impeller.
• Rhythmic thump — spray arm hitting a dish.
• Rattle — loose items or worn rack roller.
• Squeal — worn motor bearings; get it looked at.

The gradual loudness people ignore

Machines also get generally louder over years without any single identifiable noise. That is usually scale in the pump housing and narrowed spray jets changing the acoustics, plus perished insulation and mounting pads.

A deep clean with a descaling pass frequently makes an old machine noticeably quieter, which surprises people more than any other outcome of the service.