Our dishwasher is making a buzzing sound when it is supposed to be washing. I cleaned off the chopper screen and that didn't help. Thanks for your help

Here is a manual: https://dl.dropboxusercontent.com/u/8010163/Kenmore_Ultrawash_Dishwasher.pdf
I would guess that something is in one of the rotating arms jamming it. You should also check the pump clean-out because something could be in it that is locking up the motor. The other thing that can be wrong is that if the motor uses a start capacitor (cylindrical black plastic capacitor) and the start capacitor is bad. If it is a split-phase motor then the start winding could also be bad. You will need the following and a digital multimeter to check it out: https://dl.dropboxusercontent.com/u/8010163/How%20to%20use%20Test%20Equipment%20Service%20Manu al.pdf
https://dl.dropboxusercontent.com/u/8010163/Whirlpool_Kenmore%20Dishwashers.zip
https://dl.dropboxusercontent.com/u/8010163/How%20to%20Diagnose%20and%20Fix%20Everything%20Ele ctronic.pdf
https://dl.dropboxusercontent.com/u/8010163/Whirlpool%208178741%202008%20Undercounter%20Dishwa sher%20Service%20Manual.pdf
One other thing you need to check is the door switch. There is a micro-switch that detects whether the door is closed or not and it can get out of adjustment and fail to close the switch. You will then have to loosen the screws and move it so that the switch is depressed when the door lock is engaged.
I hope this helps you.