What was found
(CAN) BLEED 1 WAS CURRENTLY UNDER MEL. ONCE AIRBORNE PACK 2 SHOWED LEAKING AND FAILED INTERMITTENTLY, CABIN ALTITUDE INCREASED. FLIGHT DESCENDED TO 10,000 FT, AND RETURNED. NO EMERGENCY WAS DECLARED. INSPECTED ENGINE BLEED DUCTS AND OVERHEAT LOOPS IN PYLON AREA FOUND NR 2 ENGINE PRECOOLER BELLOWS WITH LOOSE CLAMP TIGHTENED BELLOWS CLAMP AND CARRIED OUT ENGINE PNEU OPS TEST AT 85 PERCENT N2 CKD SERVICE.