What was found
ON CLIMB OUT OF DAY FELT A SLIGHT ACFT VIBRATION (LIKE A SPOILER) RECYCLED NOT HELP- CONTINUUTE TO CLIMB AT ABOUT 12,500 HEARD AND FELT SEVERAL LOUD BANGS-LAST FOR SEVERAL SECONDS AFTER SLOWING BANGING STOPPED. RETURN TO BLOCKS, NOTICED L1 DOOR HANDLE NOT STOWED CREW DEBRIEF SAID VIBRATION FELT LIKE SPOILER FLOAT AND THAT BANGING JUST BEHIND COCKPIT. RERFORMED DETAILED VISUAL INSPECTION OF ALL FLT CONTROLS & FLAPS IAW SMP ALL CHECKED NORMAL. ACFT OK FOR SERVICE