Grinding starter

This sounds as if the starter is not disengaging. First thing to do is remove the small solenoid wire from the starter and with the key on start check that you do have twelve volts at that wire, keeping the the multi meter attached release key and voltage should drop to zero, doing this test with the wire off just isolates the started so it will not crank. Now with that checked and if okay, the problem will probably be with the starter, have it removed and bench tested. With the starter removed inspect the ring gear for wear, look for damaged teeth. Turn the engine by hand and inspect the entire drive plate. The problem is with the starter staying part engaged, the teeth on the drive plate can become damaged, and if this is the case the transmission will have to be removed to replace the drive plate.