DIAGNOSIS A grinding or metallic rattling noise almost always means something hard—a utensil, a bone, or a small dish—has fallen through the bottom rack and is interfering with the wash arm underneath.
FIX Stop the cycle. Open the door and carefully remove the bottom rack. Look down into the sump area at the bottom of the tub. You'll see the lower wash arm. Use a flashlight and feel around with your hand (watch for sharp edges) for any foreign objects. Common culprits are measuring spoons, butter knives, olive pits, or lemon seeds. Remove anything you find. Also, spin the lower wash arm by hand to make sure it rotates freely and isn't cracked or obstructed.
IF THAT DIDN'T WORK If the noise is more of a consistent humming or buzzing that happens even without a load, the drain pump might be trying to clear a blockage. Check your sink drain and air gap (if you have one) for clogs. A restricted drain can cause the pump to labor noisily.
HEADS UP Always check the silverware basket before starting a cycle. Smaller items like baby spoon handles can slip through the gaps. Consider using a utensil basket with a finer mesh or a solid bottom if this is a recurring problem.