What was found
AFTER TAKEOFF CLIMBING THROUGH 2000FT, STARTED TO ENCOUNTER MODERATE TURBULENCE AND AT THAT TIME THE MASTER WARNING CHIMED AND FUSELAGE DOORS WARNING STAYED ON FOR A FEW SECONDS. THE MASTER WARNING WENT AWAY ALONG WITH THE FUSELAGE DOOR WARNING. ON MFD DOOR PAGE ALL DOORS SHOWED GREEN INDICATION. APPROXIMATELY 2 MINUTES LATER MASTER WARNING FUSELAGE DOOR WARNING CAME BACK. CHECKED MFD DOOR PAGE AND AFT PASSENGER DOOR WAS RED. F/A REPORTED A LOUD NOISE AND CREAKING SOUND COMING FROM AFT PASSENGER DOOR. MASTER WARNING WENT AWAY AND DOOR INDICATION WENT BACK TO GREEN AFTER 2 MINUTES. F/A STATED LOUD NOISE STAYED THE WHOLE REMAINDER OF THE FLIGHT. RETURNED TO FIELD. LANDING UNEVENTFUL. CHECKED AFT PAX DO