What was found
AT 31,000 FT ALT, JUST BEFORE DESCENT NR 3 ENGINE RUMBLED TWICE AND N1 STARTED TO DECREASE. RETARDED THROTTLE TO IDLE AND N1 WAS 38 PERCENT. ADVANCE THROTTLE NO MOVEMENT ON ENGINE WHEN PASSED THROUGH 10,000 FT. ENGINE RUMBLED AND CAME BACK TO NORM. REINSTALLED BORESCOPE PLUGS AND REMOVED TURNING TOOL AND REINSTALLED COVER PLATE. REMOVED AND REPLACED FUEL FLOW TRANSMITTER REF DC-10-30MM 73-31-02-2. LEAK AND OPS CHECKS GOOD ON ENGINE RUN. REMOVED AND REPLACED NR 3 ENGINE PER W/C71T0101-3. PERFORMED ENGINE VIB CHECK PER DC10-30 M/M 72-00-00-5. ENG CHECKED NORMAL PER M/M.