As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING ENGINE START FA REPORT LOUD BANG UNDER FLOOR IN AFT GALLEY. GROUNDED - YES. T/S FOUND #1 ENGINE START VALVE INTERMITTENT. REPLACED #1 ENGINE START VALVE REF B737-800 AMM 80-11-03 STARTED #1 ENGINE TWO TIMES OPS NORMAL, NO BANG SOUND NOTED.