As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU HAS A VERY LOUD HIGH PITCH SCREAM-WHISTLE WHEN ON. BLEED VALVE POSITION DOES NOT MATTER. APU EXTREMELY LOUD. INLET AND EXHAUST NO OBVIOUS DISCREPANCIES. BLEED ON OR OFF NO CHANGE. FOUND SMALL AMOUNT OF METAL ON MAIN DRAIN CHIP DETECTOR. REPLACED APU.