Are you running brushless? I've seen brushless motors have the magnets come loose on the shaft and the make noise but they don't move much.

That or I would say rear diff also. Hold the spur gear and put one end of the car on the ground and try to drag it, it the tires won't turn the diff is ok. If the tires do tun look and see what's moving and what's not. Could be the slipper, diffs, or mabey the pinion gear is turning on the motor shaft?

rltanner and Dave_x8 ??????????????????????$$$: