What was found
(CAN) AFTER TAKEOFF, AT 11,000 FEET, A NOISE WAS HEARD FOLLOWED BY AFT CARGO DOOR OPEN WARNING. AIRCRAFT RETURNED TO DEPARTURE TERMINAL. MAINTENANCE CHECK REVEALED DOOR HANDLE POPPED SLIGHTLY. DOORS INDICATION CHECKED OK, BITE CHECK CARRIED OUT ON BOTH LANDING CONTROL INTERFACE UNIT AND GROUND PROXIMITY WARNING SYSTEM, TESTED OK.