As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU, PRIOR TO PUSH BACK WITH PACKS ON. A SMELL OF SMOKE ACCOMPANIED WITH A BANGING NOISE IT TAIL. AND VISIBLE SMOKE OBSERVCED BY GROUND CREW. NO ABNORAMAL INDICATIONS IN FLIGHT DECK. : R & R RECIRCULATION AIR FILTERS IAW AMM 21-25. REMOVED AND REPLACED APU, PERFORMED DECONTAMINATION. (8760192) AIRCRAFT WAS GROUNDED