What was found
DURING DESCENT, WHEN ACFT HAS LEVELED AND AUTOTHROTTLES ARE ADVANCED FROM IDLE, THE ACFT EXPERIENCES AN AIRFRAME SHAKING & BOOM. UNABLE TO CONFIRM WHICH ENGINE, HOWEVER IT HAPPENED 3 TIMES DURING DESCENT. PERFORMED TROUBLSHOOTING IAW FIM 71-05 F/T 808, NO DEFECTS NOTED. INSPECTED THE ENGINE, NO DEFECTS NOTED. PERFORMED AN AIRFRAME VIBRATION CONDITION INSPECTION. NO DEFECTS NOTED, RAN BOTH ENGINES TO 70 PERCENT N1, NO FAULTS NOTED.