As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON DESCENT PASSING 13000FT, CABIN & FLIGHT CREWS NOTICED A STRONG MUSTY DIRTY SOCK ODOR THAT WAS STRONGEST IN THE AFT CABIN. THE ODOR DISSIPATED WHEN THE LT PACK WAS TURNED OFF WITH CROSSBLEED CLOSED. MAINTENANCE TROUBLESHOT TO LT PACK COMPONENT CONTAMINATION. REMOVED AND REPLACED FAULTY NR 1 AIR CYCLE MACHINE.