What was found
(CAN) DURING WALK AROUND, MAINTENANCE HEARD AN UNUSUAL NOISE COMING FROM NR NR 1 ENGINE. SOUND OF BLEED LEAK, RUSHING AIR. AFTER OPENING THE THRUST REVERSER COWLS, THE TECH FOUND A RUPTURED DUCT ON THE THRUST REVERSER PRESSURE REGULATING AND SHUTOFF VALVE, PRSOV. REF IPC 78-36-00 FIG 5, PG 6, ITEM 220. DUCT WAS REPLACED AND ACFT RETURNED TO SERVICE.