As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
GROUND CREW REPORTED THAT APU MADE A LOUD BANG. APU SOUNDED DIFFERENT AFTER THAT. THE CABIN FLOOR VIBRATED THEN THERE WAS SMOKE IN THE COCKPIT. *S/D* NO CAUSE REPORTED. DENVER LINE PERSONNEL REPLACED CLAMP AFTER FLOW MULTIPLIER BYPASS VALVE. OPERATIONALLY CHECKED OK AND LEAK CHECKED OK.