When you run your dishwasher and you hear a knocking sound as it goes through the process of cleaning your dishes, you are probably hearing a problem. Dishwashers do not typically make a knocking sound, and it can indicate one of several problems ranging from a parts failure to a needed adjustment. By knowing some of the common causes of dishwasher knocking, you can diagnose the problem and get it corrected quickly.
Water Inlet Valve
The water inlet valve is the place where the dishwasher lets the water in to clean the dishes. It is located at the end of the water supply line. Like any part on a frequently used appliance, it can potentially wear out and develop too much play in the part of the valve that closes. When this happens, it can flop back and forth when the water rushes through the valve. From the outside of the dishwasher this may be detected as a knocking sound. If this is the faulty part in your appliance, it will need to be replaced to stop the noise.
Drain Hose Knock
The drain hose is a large rubber hose that carries the water away from the dishwasher tub to the main drain line in your plumbing. As the water rushes out of the tub, it can cause a vibration in the drain hose. If the drain hose was installed in a way where it can move around a lot as it passes through the cabinet wall hole, the vibration could cause the hose to knock against the edges of the hole that was cut to accommodate it or against a nearby cabinet wall. If so, the knocking sound may be detectable as the machine drains each time. This can be corrected by using caulk or putty to prevent the loose fit and preventing the vibration of the hose.
Spray Arm Interference
Sometimes the dishes are put into the dishwasher improperly. Perhaps there are too many dishes or they are stacked inside the machine in a way that allows them to interfere with the spinning spray arms of the dishwasher. If they do make contact with the dishes, resulting sound could be anything from a click to a thump or a knock. Even a clanging sound could happen with metal pots. To solve this problem, just rearrange the dishes to ensure the arm can rotate freely.
Levelling or Mounting Pads
Like a washing machine in your laundry room, the dishwasher has spinning parts. When these parts spin, it can cause the entire machine to rock back and forth slightly. If the dishwasher is off balance, it will create a very noticeable, if not loud, knocking noise. Ensure the machine is level, and install rubber mounting pads to prevent the rocking and vibration.