As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMBOUT AT 22,000 FEET AND 315 KNOTS, AIRCRAFT BEGAN VIBRATING. VIBRATION WAS FELT THROUGHOUT THE CABIN. ENGINE VIBRATION MONITORS WERE NORMAL. AIRCRAFT RETURNED TO MEM AND LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED THE LEFT FORWARD END RAM AIR INLET DOOR ACTUATOR BUSHING. OPERATIONAL CHECK OK.