As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT FL 350 MUFFLED POP SOUND HEARD IN COCKPIT. FIRST CLASS CABIN PRESS CONTROL LOST UNCOMMANDED 1500 RPM CABIN RATE OF CLIMB. PNEUMATIC SYS ISOLATED AS PER SOP AND ACFT DESCENDED TO 18000 FT, CABIN PRESS CONTROL REGAINED AS ACFT DESCENDED BELOW FL 200 MAX CABIN ALT 9000 FT. FOUND DUCT LOOSE IN ECS COMPARTMENT. REINSTALLED SAME.