DIAGNOSIS That's almost certainly something hard—a piece of glass, a bone, a utensil—that's gotten past the filter and into the wash pump area. The impeller in the pump is trying to chew it up.
FIX Unplug the dishwasher. Remove the bottom rack. Twist and lift out the cylindrical filter assembly in the sump at the bottom. Underneath, you'll see the wash pump impeller. Carefully reach in and feel around for any debris. Remove anything you find. Also, check the filter itself for tears—if it's damaged, debris will keep getting through.
IF THAT DIDN'T WORK If the noise is more of a constant, loud hum without the grinding, the wash pump motor might be seized or failing. You can sometimes check this by manually spinning the impeller you accessed after removing the filter. If it doesn't spin freely, the pump is likely shot and needs replacement.
HEADS UP Be super careful feeling around the pump impeller. The edges can be sharp. And when you reassemble the filter, make sure it's locked in place with a firm clockwise turn. An unseated filter is a major cause of performance issues.