As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
COCKPIT NOISE INFLIGHT. CREW INFLIGHT TROUBLESHOOTING FOUND THAT LT PACK WAS ALSO CAUSING PROBLEM, SEE DF842. CLEANED CTR AIR NOZZLE ASSY 23 AFT, ALL CLOGGED RESTRICTOR PLATES AND REPLACED RECIRC FAN FILTERS. FLT DECK NOISE 70 DB WITH LT FAN ON AND 72 WITH BOTH ON AND BOTH ENGINES RUNNING. RECIRC FAN IS LIKELY CULPRIT. STICKERED SWITCH PER MT 21-22-00 NOISE LEVEL WITHIN LIMITS.