What was found
PASSING 10,000 FEET IN CLIMBOUT FWD F/A REPORTED THUMP NOISE AT LEFT FWD ENTRY DOOR. WHILE CONTINUING CLIMB CAPT WENT BACK TO ACCESS NOISE/SOURCE. LEVELED AT FL230 FOR 4 MINUTES, DECIDED OK FOR CONTINUE. PASSING FL280, IN COCKPIT BOTH PILOTS HEARD LOUD THUMP AND FELT ASSOC VIBRATION THROUGH FLOORING, HALTED CLIMB AT FL290. PRESS CONTROLLER AUTO 33000, 5 PSID INDICATED. REMOVED DOOR LINER AND SIDEWALL AFT OF L1 DOOR TO INSP, NO VISIBLE DAMAGE FOUND. ADJ DOOR STOPS ON DOOR FRAME. PRESSURIZED TO 6.5 PSID.