As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MUSTY SMELL IN CABIN. DUE TO CABIN HAVING STRONG ODOR FROM APU RUNNING THE A-C PACKS, AS PER OPB, PAX FILTER FOR RECIRCULATION TO BE REPLACED ON BOTH SIDES (FIN#4012HM & 4013HM). REMOVED & REPLACED THE CARTRIDGE FILTER POSITION 4012HM AND 4013HM. OK FOR SERVICE.