What was found
WHILE CLIMBING THROUGH FL 290 A SEVERE VIBRATION COULD BE FELT IN THE AIR FRAME, AND CONTROL YOKE ACCOMPANIED BY A DEEP RUMBLE SOUND. DEPLOYMENT OF SPEED BRAKE WAS NO HELP. FLAP DAMAGE AT LEFT INBOARD AFT FLAP. INSPECTED NR 1 ENG INLET FOR (BMM) FOD DAMAGE AND NONE FOUND (71-00-0). ON POST-FLIGHT FOUND LEFT INBOARD FLAP DE-LAMINATED WITH PIECES MISSING. REPLACED LEFT AFT INBOARD FLAP IAW BMM 27-51-2. OPS NORMAL. INSPECTED AIRCRAFT NO DAMAGE NOTED.