As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIR TURN BACK DUE TO VIBRATIONS IN LEFT ENGINES AT FL 220. CREW EXPERIENCED VIBE IN YOKE AND PEDALS, AND INTENSITY WOULD INCREASE WHEN ADDING POWER. AIRCRAFT LANDED WITHOUT INCIDENT AT KHPN. REMOVED AND REPLACED NR 1 ENGINE, IAW AMM 71-00-01.