What was found
WHEN REDUCING POWER LEVERS FROM CLIMB TO CRUISE THRUST, ENGINES DEVELOPED A HARMONIC RESISTANCE RESULTING IN AIRCRAFT SHAKING AGGRESSIVELY. SHAKING STOPPED WHEN POWER WAS PULLED BACK DOWN TO 85 PERCENT N1. REMOVED AND REPLACED NR 2 ENGINE HMU AND AIRCRAFT VIBRATION MONITOR, (P/N 6672M213), (S/N DA72) PER MM.