Motor and Motor Fan Are Running
The motor makes a constant, low humming sound while the dishwasher is running. The noise is more noticeable if you do not have any sound insulation installed around the dishwasher. A fan, which also makes a humming sound, blows on the motor to keep it cool when temperatures begin to rise.
Soft-Food Disposal Is Running
Some KitchenAid dishwashers may be fitted with a soft-food disposal to reduce the size of large food chunks before they pass into the plumbing and cause a blockage. The disposal makes a low humming sound and usually runs when the dishwasher is pumping out water a few times each cycle.
Pumps Are Running
The dishwasher pumps water in and out of the appliance several times during each cycle, each time making a gently humming or roaring noise. The noise lasts a few seconds each time and is not cause for concern. You may also hear a gurgling noise with the hum as water exits down the drain.
Fault
Stop the dishwasher and cancel the current cycle; the appliance should fall silent once the water has been pumped out of the tub. There may be a problem with the appliance if the hum continues while the dishwasher is idle. Call for repair if the noise cannot be attributed to any of the above causes.