As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PIT - FLT 0521 - THE CAPTAIN REPORTED A LOUD POPPING OR SNAPPING NOISE ON CLIMB-OUT. AT THE SAME TIME THE MAIN DOOR ANNUNCIATOR LIGHT ILLUMINATED. CAPTAIN DECIDED TO RETURN TO PIT. MAINTENANCE REPLACED THE FORWARD ENTRY DOOR SWITCH. OPERATIONS CHECKED NORMAL. (Z)