Diagnosis
That's almost certainly something hard—a piece of broken glass, a bone, a utensil—that's gotten past the filters and is now in the circulation pump impeller. The impeller is plastic, and grinding against a hard object makes that awful noise.
How to Fix It
Unplug the machine. Remove the lower rack and both filters (the fine mesh and the coarse flat filter). Shine a flashlight down into the pump sump at the bottom. You'll likely see the offending object. Use long-nose pliers or tweezers to carefully extract it. Rotate the pump impeller by hand (it's in the center of the sump) to feel for any remaining obstruction or damage. If it spins freely, you're probably good.
If That Didn't Work
If you can't see anything but the noise persists, the impeller itself might be cracked or have a broken blade. That requires removing the pump assembly, which is a more involved repair. Also, while rare on this model, a worn bearing in the wash motor can cause a grinding sound, but that's more of a constant rumble than a violent grinding.
Heads Up
Before every load, do a quick check for small, hard items. That little "grinding" event can crack the impeller housing, which then leads to a leak. If you run it and hear the noise again immediately, stop the cycle to prevent more damage.