If your dishwasher is getting loud or making a weird noise, you should check the heater fan, motor, water-inlet valve, and pump. Sometimes the bearings in the heater fan may get worn out or rust. If this happens, it may become very noisy, either grinding on the bearings, or scraping against the rust. If this happens you need to replace the fan motor. Sometimes, a fan blade may come loose, and you need to replace it.
Sometimes it’s the motor that makes the noise you hear. The motor has bearings in it which may become worn or get rusty. When the bearings get worn, they allow the shaft to wobble which can get quite loud. If there is a spin seal leak, water may get inside the motor, washing the bearing grease away. If the spin seal is leaking, you’ll notice water leaking from under the dishwasher.
There is also a disc attached to the top of the motor called a slinger. It sometimes breaks off and spins around the motor's shaft while it turns, causing some noises. You will need to replace the motor if the bearings are bad. You also need to replace the motor if the slinger is broken as well.
Newer dishwashers may make a squealing or rattling noise on the first run. This is because it has not had any water in it yet, and the motor seals are dry. You may hear this in a unit that hasn't been run in a week or more as well. You should operate the dishwasher regularly to keep the sump water from getting smelly, and to keep the seals lubricated. You can add a quart of water to the sump before running it.
Rattling noises may be produced by dishes rattling inside the dishwasher due to the water pressure from the sprayer arms on the dishes. To determine if the rattling is a loading issue, run the unit empty. If the sound is persistent, it may be that there is debris in the pump.
dishwasher water-inlet valves are noted to make a hum that lasts about 60-90 seconds several times during a washing cycle. This hum is a different hum than the sound of the motor running.
A rhythmic knocking or thumping sound may be caused the sprayer arms hitting something as they go around and around. Rearrange the dishes and resume the wash.
A clunking or clanking may be heard when the detergent cup or detergent dispenser opens; while a clicking sound may be produced by the timer or electronic control panel.
A solenoid makes a snap sound when it opens. This happens about six times during each load.
Pipes rattling or banging may be caused by a water hammer effect. Water hammer sounds are caused by a valve closing in the system, and yet the water in the pipe is still flowing because of its kinetic energy. The sound is caused by the water slamming into the closed section of pipe. A plumber can install an anti-hammer device.
Small objects can sometimes get stuck in the pump. When this occurs, you’ll need to open the pump and then remove the item that is making the noise or replace the pump. The dishwasher pump is usually mounted directly to the motor and runs off the motor as well. The pump is also attached to the bottom of your dishwasher.