As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHEN THE FLIGHT/TAXI SWITCH WAS SELECTED TO FLIGHT MODE PRIOR TO DEPARTURE, A LOUD BANG WAS HEARD IN THE CABIN BY THE F/A AND FLIGHT CREW. ALSO NOTED A RAPID LOSS OF HYD FLUID IN THE NR 1 SYS. ACFT RETURNED TO APRON. MX FOUND THE LT IB ROLL SPOILER ACTUATOR CASING HAD CRACKED CAUSING THE FLUID LOSS. ACTUATOR WAS REPLACED AND ACFT RETURNED TO SERVICE.