As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF ON FLIGHT 3356, CREW NOTED A STRANGE NOISE AND VIBRATION AFTER TAKEOFF. IN-FLIGHT VIBRATION, LAV SERVICE DOOR OPENED IN-FLIGHT. FLIGHT RETURNED TO DTW. MAINTENANCE INSPECTED LAV SERVICE DOOR FOUND TO BE IN SERVICEABLE CONDITION. LATCHES LOCK OVERCENTER PROPERLY AND DOOR IS SECURE TO AIRFRAME. ALL CHECKS GOOD AT THIS TIME.