As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE CREW REPORTED AFTER APU START RECEIVED ARUAL WARNING UNIT 1 CHANNEL AND SMOKE BEGAN POURING OUT OF OPENING PLUS ABOVE FMS NR 2. THE ACFT WAS SHUTDOWN AND SMOKE STOPPED. MX INSPECTED AND PERFORMED OPS CHECKS OF BLEED SYS. OPS CHECKS WERE GOOD AND NO SMOKE WAS NOTED AT THIS TIME. THE ACFT WAS RELEASED FOR SERVICE.