What was found
AT CRUISE FL370, NOTICED LOUD NOISE COMING FROM FORWARD AIRCRAFT LEFT, SUSPECTED LEAKY DOOR SEAL. CABIN ALTITUDE DISPLAYED 9100 WITH A SLIGHT CLIMB AND OUTFLOW VALVE POSITION FULLY CLOSED. CABIN ALTITUDE CONTINUED TO CLIMB TO 9500. MOVED SELECTOR FROM AUTO 2 TO AUTO 1 WITH NO CHANGE. DESCENDED TO FL330, CABIN ALTITUDE DECREASED AND STABILIZED AT 8700 WITH OUTFLOW VALVE STILL IN FULLY CLOSED POSITION. MDC DOOR SEAL REPAIRED IAW AMM 52-09-00-8 .