What was found
MCO/LGW - FLT 504 - PILOT REPORTED 'AIRFRAME VIBRATION FELT IN FLOOR AND FLIGHT CONTROLS ABOVE 180 KNOTS ON TAKEOFF, CLIMB, CRUISE AT FL 270 AND DESCENT. IT NOTICEABLY DECREASED AFTER FLAPS LOWERED TO 22 DEGREES AND SLOWING BELOW 175 KNOTS.' THE CAPTAIN RETURNED BACK TO MCO AND LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE RELATCHED THE APU SERVICE DOOR. A TEST FLIGHT WAS FLOWN WITH NO DEFECTS NOTED. AIRCRAFT RETURNED TO SERVICE.