What was found
SDR WRITTEN TO CLOSE SDR U30A200600003, WHICH READ: FLT 1013 CUN-STL; SHORTLY AFTER T/O, CREW REPORTED VIBRATION, POPPING SOUNDS COMING FROM NR 2 ENG. ENGINE ROLLED BACK TO IDLE. CREW MANINTAINED IDLE CONDITION (ENGINE PARAMETERS WERE NORMAL AND OIL QUANTITY GOOD). CREW DECLARED AN EMERGENCY, RETURNED AND LANDED W/O FURTHER INCIDENT. AFTER TOUCHDOWN. NR 2 ENG. WAS SHUTDOWN, TAXIED SINGLE ENG TO PARKING. MAINT WAS DISPATCHED WITH BOROSCOPE EQUIPMENT TO DETERMINE ENG CONDITION. TROUBLESHOOTING SUGGESTS NR 4 BEARING FAILURE. ENGINE CHANGE IS LIKELY. ENGINE WAS REMOVED, REPLACED. ENGINE WAS REPAIRED, DUE TO NR 4 BRG DETERIORATION. ENG HAS BEEN RETURNED TO SERVICE. SDR U30A200600008 CLOSES SDR U30A200600003.