What was found
SHORTLY AFTER TAKE OFF, CREW REPORTED VIBRATION AND POPPING SOUNDS COMING FROM NR 2 ENGINE. ENGINE ROLLED BACK TO IDLE. CREW MAINTAINED IDLE CONDITION (ENGINE PARAMETERS WERE NORMAL & OIL QUANTITY GOOD). CREW DECLARED AN EMERGENCY & RETURNED TO CUN, AND LANDED W/O FURTHER INCIDENT. AFTER TOUCHDOWN, THE NR 2 SHUTDOWN & TAXIED SINGLE ENGINE TO PARKING. MAINTENANCE PERSONNEL WERE DISPATCHED, WITH BOROSCOPE EQUIPMENT TO DETERMINE ENGINE CONDITION. TROUBLESHOOTING SUGGESTS NR 4 BEARING FAILURE. ENGINE CHANGE IS LIKELY. (OPEN)