As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
VIBRATION IN BOTH CONTROL YOKES STARTING AROUND 200 KTS INCREASING IN INTENSITY THRU 220 KTS SLOW TO BELOW 200 KTS. RETURNED TO FIELD LANDING UNEVENTFUL. TENSIONED AILERON CABLES, REPLACED WORN BUSHINGS IN RT INBD AND OTBD SPOILER LINKAGES, REPLACED NR 1 PROPELLER DUE TO OUT OF BALANCE. RETURNED TO SERVICE.