What was found
IN CRUISE, STARTED STEP CLIMB FROM FL370 TO FL390, 1L CABIN DOOR THEN BEGAN TO HAVE VERY LOUD NOISE COMING FROM UPPER FWD PORTION OF DOOR. CORRECTIVE ACTION: INSPECTED L1 DOOR SEAL AND FOUND A CUT AT UPPER FWD EDGE. REMOVED AND REPLACED L1 DOOR SEAL, IAW A319 AMM 52-11. PRESSURIZED AC AND FOUND NO LEAKS OR NOISE FROM SEAL.