As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) DURING A TEST FLIGHT TO TEST THE RH FLOW PACK WHILE CLIMBING OUT THROUGH 5000 FEET, THERE WAS A SCREAM IN THE CABIN. MAINTENANCE PERFORMED AN INSPECTION OF THE PRESSURIZATION DUCTING INSIDE THE CABIN AND FOUND THAT A FLAPPER VALVE HAD DISLODGED ITSELF INSIDE THE DUCTING AND WAS CAUSING THIS WHISTLE "SCREAMING" NOISE. THE VALVE WAS REPLACED AND AIRCRAFT WAS RELEASED FOR A TEST FLIGHT.