As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
TWICE ON DESCENT WHEN REDUCING ENGINE POWER THERE WAS A STRONG VIBRATION AND RUMBLING SOUND. VIBRATIONS IN YOKE AFTER POWER REDUCED FOR INITIAL DESCENT & FINAL APPROACH, DURATION OF 2-3 SECONDS TWICE AUTOPILOT WAS ENGAGED BOTH TIMES, ENGINE PARAMETERS NORMAL, NO STICK SHAKER WARNING NOTICED. REPLACED NR 1 ENGINE IDG DUE TO INFORMATION WITHIN SERVICE TIP. IDG REPLACED PER MM.