What was found
THE FLIGHT RETUNED TO CUN AND AN UNEVENTFUL SINGLE ENGINE LANDING. THE NR 1 ENGINE STALLED AND FAILURE SHORTLY AFTER TAKE-OFF. THE FLIGHT CREW HEARD THE LEFT ENGINE POPPING AND FELT A SHUDDER DURING THE CLIMB OUT. THIS WAS ACCOMPANIED BY ENGINE PARAMETERS ROLLING BACK. THE NR 1 ENGINE WAS SHUT DOWN, PER THE QRH. CORRECTIVE ACTION: MAINTENANCE FOUND METAL IN THE TAILPIPE UPON ARRIVAL BACK AT THE GATE. THE ENGINE WAS REPLACED.