What was found
DIRTY SOCK ODOR COMING FROM PACKS, ON GROUND AND WHEN AT IDLE IN DESCENT. NO DIFFERENCE BETWEEN ENGINE OR APU BLEED. INBD CREW FAILED TO NOTIFY CONTROLLER CENTER ON ARRIVAL OF THIS DISCREPANCY. RAN PACKS WITH APU, INSPECTED SUPPLY DUCTS FOR RECIRCULATION AND MIXER UNIT IAW AMM 21-21-00-210-804-A, REPLACED RECIRCULATION FILTERS IAW AMM 21-21-41/401, NO DIRTY ODOR NOTED. OK TO CONTINUE.