As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIR RETURN DUE TO VIBRATION FELT INFLIGHT. INSPECTED ALL COMMON AREAS ON AIRCRAFT THAT CAUSE VIBRATION. FOUND NOTHING THAT COULD VIBRATE. AFTER REMOVING LT SPINNER FOUND ROUGHLY A 1/4 POUND OF GREASE BUILT UP ON ONE SIDE OF SPINNER. ALSO FOUND ONE DE-ICE LEAD BROKEN AND SUSPECT ICING BUILD UP THAT THREW PROP OUT OF BALANCE. INSPECT LT AND RT PROP HUBS FOR OIL.