DIAGNOSIS Something has almost certainly fallen through the filter and is now in the drain pump area. A small piece of glass, a bone, or a cherry pit are the usual suspects.
FIX You need to get to the drain pump. First, unplug the dishwasher. Remove the lower rack. Then, unscrew and lift out the fine mesh filter and the coarse filter underneath. You'll see the drain pump cover (a round plastic piece) at the bottom. Carefully unscrew it (it might just be a quarter-turn). Reach in with a flashlight and needle-nose pliers to feel for and remove any debris. Reassemble everything in reverse order.
IF THAT DIDN'T WORK If you find nothing or the noise persists after clearing debris, the drain pump impeller itself could be damaged or have a worn bearing. That would require replacing the drain pump assembly.
HEADS UP Always scrape plates well before loading. The filter system is excellent, but it's not a garbage disposal. That grinding noise is the object hitting the pump impeller—if you let it go, it can eventually burn out the pump motor.