What was found
AIRCRAFT HAS BAD VIBRATION THROUGH YOKE & RUDDER PEDALS. VIBRATION GETS MUCH WORSE WITH INCREASE IN AIRSPEED. POWER SETTINGS MODE MADE NO DIFFERENCE. TROUBLE SHOT THE DISCREPANCY TO A DEFECTIVE RUDDER LOWER TRIM TAB HINGE PIN THAT BACKED OUT CAUSING THE VIBRATION IN FLIGHT. RUDDER ASSEMBLY WAS REPLACED DUE TO DAMAGE CAUSED TO HINGE FROM VIBRATION. A SUCCESSFUL OPERATIONAL CHECK FLIGHT WAS PERFORMED. ACFT WAS RETURNED TO SERVICE.