I have a Maytag Quiet series dishwasher (dont' remember which model but I bought it last year. I press 1 button and it does all the cleaning by itself - has built in "dirty water" sensor to know if it needs to continue washing or not). But its always been a noisy washer. Every so often it makes a grinding noise that lasts anything from 10 seconds to the entire wash cycle.
9 months after putting up with the grinding noise, which was getting progressively worse, I decided to call Maytag, and a technician came over and said that it was a known issue with my model that had defective motors, and that they would replace the motor for free (wich they did). Replacing the motor helped reduce the grinding noise, but it is still present every now and then, just not as frequently or as loud.
Please reply if you find out what is causing this noise, as I'm having it as well, but at this point I'm assuming its an issue with the dishwasher design itself. When I put in plates I make sure that there are no hard food objects inside, so at this point I don't think its food particles (ex: shells, nuts, etc.) causing the grinding noise.