Diagnosis
That grinding noise is typically the metal drive stud on the base rattling against the plastic drive socket on the pitcher because the coupling is worn or there's debris in the socket.
How to Fix It
Unplug the unit. Remove the pitcher and look inside the black plastic drive socket on its bottom. Use a damp cloth or a cotton swab to clean out any dried food or residue. Next, look at the silver metal drive stud on the base. Wipe it clean and make sure it isn't bent. When you re-seat the pitcher, press down firmly and twist slightly to ensure a tight fit.
If That Didn't Work
The noise could be coming from inside the blade assembly. Unscrew it from the pitcher and check if the bearing is loose or if the blades themselves are wobbly. A worn blade bearing will make a consistent grinding sound.
Heads Up
Running it with a persistent grinding noise will accelerate wear on both the pitcher socket and the base's drive stud. If cleaning doesn't fix it, the pitcher likely needs replacement.