As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN)PILOT REPORTED THAT N1 TACHOMETER INDICATOR FLUCTUATES ERRATICALLY, APPROXIMATELY 1 OR 2 PERCENT IN CRUISE. TACHOMETER REMOVED FROM THE ENGINE. INSPECTION REVEALED THE DRIVE SHAFT WAS STIFF TO TURN AN D GRINDING COULD BE HEARD FROM INSIDE THE UNIT. TACHOMETER REPLACED AND ENGINE GROUND RUN SERVICEABLE.