As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
REPORT FAINT MUSTY SMELL WHEN CLIMBING FROM 6000 FEET THROUGH 13000 FEET. SMELL WENT AWAY AND CAME BACK DESCENDING THROUGH 13000 FEET AND WENT AWAY AGAIN THROUGH 10000 FEET. REPLACED RECIRCULATION FILTER, FOWARD PIT LEFT HAND SIDE. OPS CHECK NO SMELL.