What was found
DURING ENG START APU BLEED VALVE APPEARS TO MAKE NOISE HEARD AT DOOR 3&4. OPENED ACCESS TO LT F/A CREW REST AREA, LT SIDE OF AFT CARGO PIT, MAIN GEAR DOORS, AND APU AREA. INSPECTED ALL DUCTS FROM MLG BULKHEAD TO APU. FOUND LOOSE DUCT AT EXHAUST DUCT ADP1, SECURED DUCT CHECKED SYSTEM WITH PRESSURIZED BY ADP. NO NOISE VIBRATION NOTED, PRECAUTIONALLY CHECKED APU DUCT FROM APU ISOLATION DUCT TO WHEEL WELL-NO LEAK NOTED. ALL DUCTS SECURE IN NORMAL CONDITION. PERFORMED 2 ENG START, FOLLOWED BY 1 ENG AT A TIME, THEN 2 ENG START W-PACKS ON, AND FINALLY 2 ENG NORMAL START. NO ABNORMAL NOISE NOTED.