As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB, CREW NOTED A LOUD SQUEAL FOLLOWED BY A POP AND A STEADY LOSS OF CABIN PRESSURE (ABOUT 2000 FPM). EMERGENCY PROCEDURES WERE EXECUTED AND EMERGENCY WAS DECLARED. ACFT LANDED SAFELY. MX INSPECTED THE ACFT AND FOUND THE MAIN ENTRY DOOR SEAL HAD COME LOOSE. THE DOOR SEAL WAS REATTACHED.