What was found
REPEAT WRITE UP HIGH PITCH CONTINUOUS TONE, FROM CAPTAIN SIDE BELOW LEFT FOOT. CAB ALT 5800 FT DP 8.5. WENT TO MANUAL ON OUTFLOW VALVES, REDUCED CAB ALT TO 5000 FT TONE DP 8.3, THE TONE WAS NOTICEABLY QUIETER. AFTER APPROXIMATELY 10 MINUTES WE RESELECTED AUTO ON THE OUT FLOW VALVES, THE TONE CONTINUED FOR ANOTHER 10 TO 15 MINUTES, THEN STOPPED. CAB ALT RETURNED TO 5900FT AND DP 8.5 NO FURTHER NOISE FOR REMAINDER OF THE FLIGHT. REPLACED FWD ACCESS DOOR SEAL REF B777 MM 52-09-05-2. INSTALLED FWD ACCESS DOOR REF B777 MM 52-48-01-4. PRESSURIZE CABIN REF B777 MM 05-51-24-2, FWD ACCESS DOOR SEAL LEAK CK OK.