What was found
IN DESCENT, BOTH PACKS ON AND ENGINE & WING ANTI ICE ON, AIR FLOW THRU DUCTS WAS VERY LOUD. PACK FLOW INDICATION ON ECAM, BOTH AMBER AND LOW FLOW POSITION. CONDITIONED AIR SMELLED HOT. BOTH TAKEOFF AND LANDING. PERFORMED OPS TEST OF PACKS IAW AMM 21-51-00. NO NOISES OR HOT SMELL FOUND. INSPECTED DUCTS AND FOUND LARGE LEAK ABOVE APU DUCT CHECK VALVE. REPLACED SEAL ABOVE CHECK VALVE IAW AMM 36-12-12/401. OPS AND LEAK TEST GOOD.