As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
F/A-S REPORT NOTICEABLE HUMMING SOUND IN CENTER OF A/C GEAR AREA. HEARD IN COCKPIT FAINTLY. FA SAY NOISE-HUMMING SOUND MORE PRONOUNCED IN CENTER OF FIRST CLASS. IN INTENSITY..FL370IN CRUISE STABLE AIR-SPEED. REPORTED BY F/O IN CRUISE CHECK HUMMING NOISE COMING FROM BELLY OF A/C NOT DOOR AREAS. FIRST CLASS AREA, SOUND VARYING. REQUEST CREW COMMENTS. COULD NOT CHANGE VALVE DUE TO NO O-RING SENT. PCN 756-2184. REPLACED SKIN AIR INLET VALVE PER AMM, OPS CHECK GOOD.