[Eyegore]

I agree with Matt, I just had the same problem, the grinding is the motor. I had a shop replace the motor I pulled out from the wrecking yard, $32 for the motor, $30 to install. If your mechanically inclined you could do it yourself, remove the window glass, vent window assembly then the whole regulator with the motor attached.
When the assembly was out we bench tested the motor to make sure that was the culprit, it was. Reinstalling everything was more difficult, getting the glass back on the regulator track was the toughest part as I watched on. But after watching I believe I could tackle this on my own. If you do try t do it yourself just remember to remove all brackets, espically in the opening behind the door latching mechanism, that opening is where the regulator with and motor will come out. Or you could just check with a glass shop or wrecking yard that replaces glass, they'll probably do everything for $120, that the other quote I got for fixing it.