As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW NOTICED THAT WHEN THEY ENGAGED THE PARKING BRAKE, A VERY LOUD SQUEALING NOISE COMING FROM THE NOSE AREA, WHICH IS THE LOCATION OF THE EMERGENCY PRESSURE REDUCING VALVE. CHANGED VALVE, PROBLEM SOLVED. SUSPECT INTERNAL LEAKAGE OF VALVE.