As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
VERY HIGH PITCHED SQUEAL IN FRONT, LT SIDE OF COCKPIT. SOUNDS LIKE A PRESSURE LEAK. CREW NOTED SOUND EMANATING FROM LT SIDE OF COCKPIT AT FLOOR, ORIGINS UNCERTAIN. FOUND UN-USED PORT ON GASPER MANIFOLD UNDER CAPTAINS SIDE FLOOR CAP UNSECURED. REINSTALLED CAP, NO LEAKS OR NOISE NOTED.