DIAGNOSIS A foreign object is stuck in the wash arm circulation pump. Common culprits are lemon seeds, cherry pits, or broken glass.
FIX Unplug the dishwasher. Remove the lower rack and filter assembly. Manually rotate the wash impeller in the sump. It's the silver or white plastic star-shaped piece. Feel for obstruction. Use needle-nose pliers to remove any debris you find.
IF THAT DIDN'T WORK The wash pump motor bearings are failing. If the impeller spins freely but the grinding persists during operation, the pump motor assembly needs to be replaced.
HEADS UP Always scrape plates, don't rinse. But check for small hard objects like pits before loading. They bypass the filter and go straight to the pump.