As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
GEG - AFTER STARTING APU NOTICED SMOKE IN CABIN. NO DEICING HAD OCCURRED. NO PASSENGERS ON BOARD AT THE TIME. PLACED THE APU ON MEL 49-00-1. RETURNED TO SERVICE. MEL CLEARED 3/25. REMOVED APU AND INSTALLED SERVICEABLE APU IAW MTC 6492001. RETURNED TO SERVICE.