As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DESCENT FROM FL 360 UPON INITIAL THRUST REDUCTION BOTH PILOTS HEARD A "POP" WITH A SMALL VIBRATION. BOTH ENGINE PARAMETERS LOOKED NORMAL HOWEVER NR 1 RETARTED QUICKLY TO 31% N1, WHILE NR 2 SLOWLY RETARTED TO 42% N1 WITH A GRADUAL REDUCTION (15-20 SEC) TO 30-31% N1. THRUST LEVERS HAD SPLIT OF 1-3 KNOB WIDTHS AT VARIOUS SPEEDS. REMOVED AND REPLACED NR 1 ENGINE PER MT.