As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING PREFLIGHT A LOUD BANG & POPPING SOUND WAS HEARD INSIDE & OUTSIDE OF ACFT. A BURNING SMELL WAS IN THE COCKPIT FOR ABOUT 30-45 SECONDS. INSPECTED & VERIFIED EE COOLING SYS IN & OUT FAN MOTOR VLV DUCTS, NO DEFECTS NOTED. CLEANED EE COOLING SYS CLEANER ON CMC EE COOLING SYS. TEST PASSED IAW MM 21-58-00 FOUND NO BURNING SMELL.