What was found
CREW REPORTED A LOUD BANGING NOISE IN FLIGHT. CREW ELECTED TO RETURN TO BHM AND LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED AND FOUND REFUEL DOOR OPEN AND CAP MISSING. MAINTENANCE FOUND NO EVIDENCE OF ENGINE INGESTION OR OTHER STRUCTURAL DAMAGE. MAINTENANCE SECURED THE DOOR CLOSED AND REPLACED THE MISSING FUEL CAP IN ACCORDANCE WITH THE AIRCRAFT MAINTENANCE MANUAL. AIRCRAFT WAS RELEASED FOR SERVICE.