As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED VIBRATION AT START-UP AND SHUT DOWN. INSPECTION FOUND RT LOWER ENGINE MOUNT TO FIREWALL BOLT LOOSE. FURTHER INSPECTION FOUND BOLT GRIP LENGTH TOO LONG AND NUT BOTTOMED ON THREADS. ADDED WASHER UNDER NUT TO TAKE UP SPACE. RESEARCH OF RECORDS FOUND BOLT HAD NEVER BEEN REMOVED OR REPLACED.