As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PITCH VIBRATION IN FLIGHT CONTROLS WITH AUTO PILOT ON, VIBRATION INCREASED AS SPEED INCREASED. NOTICED AT 250 KTS AND 10000FT, VIBRATION ALSO COULD BE HEARD AS LOW FREQUENCY SOUND. TIGHTENED LT ELEVATOR BUNGEE AND ADJUSTED ELEVATOR CABLE TENSION IAW CESSNA 750 MM 27-30-00.