As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DIRECTIONAL GYRO PRECESSES ABOUT 5 DEGREES EVERY 10 MINUTES IN-FLIGHT. WITH VACUUM SYSTEM TEST KIT INSTALLED, DG PRECESSES ABOUT ONE-HALF DEGREE EVERY 15 MINUTES. ON THE NEW CESSNA AIRCRAFT, THE INSTRUMENTS AS WELL AS THE INSTRUMENT PANEL ARE HARD MOUNTED TO THE AIRFRAME. SUBMITTER SUSPECTED THE VIBRATIONS CAUSED BY THE RUNNING ENGINE ARE TRANSMITTED DIRECTLY TO THE INSTRUMENTS AND ARE THE CAUSE OF THE PROBLEM. (X)