As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APPROX 2 HOURS AFTER TAKEOFF, LOUD VIBRATING NOISE REPORTED ROW 13 ACFT RT. NOISE APPEARED COMING FROM OVERHEAD POSITION & FELT OVERHEAD & IN FLOOR BELOW. NOISE IS HIGH PITCHED & CONSTANT, GETTING LOUDER AT 4:50 INTO FLIGHT. FOUND INSPECTION PANEL ON PACK 2 PLENUM CHAMBER TO BE MISSING FROM ITS PROPER INSTALLATION. REINSTALLED WITH NEW HARDWARE.