As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE APU RUNNING HEARD LOUD BANG NOISE FROM REAR OF AIRCRAFT. APU RPM DROPPED BY 10 PERCENT. FLIGHT ATTENDANT NOTICED SMELL OF FUEL IN REAR OF AIRCRAFT. NO INDICATION OF FIRE. SHUTDOWN APU. INSPECTED APU, FOUND LOOSE B-NUT ON FUEL SOLENOID. RETORQUED B-NUT. NO FURTHER FUEL LEAKS NOTED. ATTEMPTED TO START APU. HAGS AT 49 PERCENT, PLACED ON MEL. (K)