As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT CRUISE FLIGHT AT FL380, RECEIVED A LEVEL 3 CABIN ALTITUDE. QRH ACTION AVIONICS FAN OVRD CORRECTED PROBLEM. AFTER APPROX 10 MINUTES PROBLEM RETURNED. HAD TO INITIATE DESCENT TO FL320 TO MAINTAIN PRESS. THERE WAS A SLIGHT VIBRATION UNDER THE CAPTAIN'S FLOOR AREA. REPLACED OUTFLOW VLV ACTUATOR.