As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(LOG 8395700) WHILE AT THE GATE JUST PRIOR TO PUSH FLIGHT ATTENDANTS REPORTED A KNOCKING SOUND IN AFT GALLEY. NOISE AND VIBRATION COULD ALSO BE FELT IN THE COCKPIT. THERE WAS ALSO A SLIGHT ODOR OF EXHAUST. VERIFIED APU AT FAULT, MCD FULL OF METAL. VERIFIED NO OIL CONTAMINATION IN BLEED DUCT. PERFORMED DUCT BURN AND RECIRCULATION FILTER REPLACEMENT AS PRECAUTION. ALL NO GO ODI PROCEDURES C/W.