What was found
F/A NOTIFIED US OF A VERY LOUD AIR NOISE COMING FROM THE L1 DOOR STARTING AT ABOUT 5,000' ALTITUDE. THE F/O INSPECTED THE DOOR VISUALLY AT 25,000 FT AND SAW DAYLIGHT COMING FROM / NEAR THE UPPER HINGE ON THE FORWARD PART OF THE DOOR SEAL AREA. THE PRESSURIZATION FUNCTIONED AND OPERATED NORMALLY THROUGHOUT THE FLIGHT. GROUNDED - YES. DEBRIEFED FLIGHT CREW, F/O SAID LOUD SQUEAL AT L-1 DOOR UPPER HINGE AREA. FOUND L-1 DOOR UPPER HINGE FLAPPER DOOR SEAL BENT AND RUBBER SEAL CUT. REMOVED AND REPLACED FWD ENTRY DOOR FLAPPER SEAL (UPPER), REF B737-800 AMM 52-11-00-020-801, 52-11-00-420-801. PRESSURIZED AIRCRAFT, NO LEAKS NOTED. PERFORMED GVI OF L-1 DOOR, SEAL, SILL, AND SURROUNDING AREA - NO DEFECTS NOTED.