What was found
CLIMBING THROUGH FL300 AT .77 WE ENCOUNTERED AIRFRAME VIBRATION. IAW QRH 56.18 WE DISCONNECTED AUTOPILOT 1 & APPLIED LT RUDDER, WHICH DAMPENED THE VIBRATION. UPON DELETION OF VIBRATION WE RE-CONNECTED AUTOPILOT 1 WHILE CRUISING AT FL 250 & M.78 WE RE-ENCOUNTERED VIBRATION & APPLIED PREVIOUSLY MENTIONED PROCEDURE. THIS OCCURRED TWO DIFFERENT TIMES. PERFORMED POST FLIGHT INSPECTION OF AIRFRAME, CHECKED WINGS, ENGS FUSELAGE & TAIL SECTION FOR APPARENT LOSS OF DAMAGED PANELS. NO DEFECTS NOTED AT THIS TIME. ACFT OK FOR RETURN TO SERVICE IAW AMM 05-50-00.