As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ATL - CREW REPORTED SMOKE IN CABIN. EMERGENCY DECLARED RETURNED ATL WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. CLEANED AUXILIARY POWER UNIT INLET. ACCOMPLISHED BURNOUT OF HIGH PRESSURE PNEUMATIC DUCTING. SYSTEM GROUND CHECK NORMAL OPERATION.