As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHORTLY AFTER TAKEOFF WHEN AIR CONDITIONER WAS TURNED ON, THE PILOT HEARD A LOUD NOISE. RETURNED TO BASE AND LANDED WITHOUT INCIDENT. MAINTENANCE FOUND DUCT HOSE HAD BLOWN OFF. REPLACED SAME. REF: AIRESEARCH MANUAL 4-379, FIGURE 6, ITEM 20.