As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WITH APU RUNNING ON THE GROUND & WITH THE ENGINES OFF, HAD SMOKE IN THE AFT CABIN. COMPLETED PRELIMINARY INSPECTION OF APU & RELATED PLUMBING. RAN APU , CONTACT BLEED AIR SUPPLIED FOR 1.0 WITH NO INDICATION OF SMOKE IN THE AFT CABIN OR SMOKE ODOR IN ACFT. ALL WORK ACCOMPLISHED IAW MM 49-20-00. NO FURTHER ACTION REQUIRED.