As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: DURING CLIMB OUT THERE WAS A SLIGHT MUSTY ODOR. WE TURNED PACK 1 OFF AND THE ODOR WENT AWAY. UPON LANDING THE ODOR WAS NOTICEABLE AGAIN. NO REPORTED ODOR IN THE CABIN. MAINTENANCE REPLACED THE RECIRCULATION HEPA FILTERS PER AMM 21-21-41. A SATISFACTORY OPERATIONAL CHECK WAS ACCOMPLISHED WITH NO ODORS NOTED.