As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED DUE TO: LEVELING OFF AT FL310 NUMBER 1 ENGINE N1 DIPPED AND SURGED AT LEAST 3 TIMES. THIS WAS ACCOMPANIED BY A BANGING NOISE HEARD IN THE COCKTAIL. FLIGHT ATTENDANT REPORTED SEEING SPARKS COMING FROM THE NUMBER ONE ENGINE AS WELL. ALSO HEARD AN AUDIBLE BANGING SOUND, AND REPORTED FEELING THE CABIN FLOOR VIBRATE. AIRCRAFT AIR INTERRUPTED BACK TO AND LANDED SAFELY AT ORD. REMOVED AND REPLACED NUMBER 1 ENGINE ASSEMBLY. PER JC 08L40072003.