As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED DUE TO: UNKNOWN VIBRATION IN TAIL SECTION OF AIRCRAFT, FELT IT IN THE RUDDERS AND ELEVATORS. AIRCRAFT AIR INTERRUPTED BACK TO AND LANDED SAFELY AT MIA. ACCOMPLISHED GENERAL VISUAL INSPECTION OF THE AIRCRAFT AND FOUND APU INLET DOOR OPEN. SECURED APU INLET DOOR IN THE CLOSED POSITION. PER AMM 49-15-00.