What was found
IAH - FLT NR 2522 - AFTER TAKEOFF, UPON RETRACTION OF LANDING GEAR A LOUD RUMBLING NOISE WAS HEARD. FLIGHT CREW CYCLED LANDING GEAR, NOISE CONTINUED. AIRCRAFT RETURNED TO IAH AND LANDED WITHOUT INCIDENT. MAINTENANCE REMOVED AND REPLACED SEQUENCE VALVE FOR RT MLG INBOARD FORWARD DOOR. PERFORMED OPERATIONAL CHECK, NO DEFECTS NOTED. A/C RETURNED TO SERVICE. (M)