What was found
ON APPROACH, AT 122 KNOTS, EXPERIENCED A VIBRATION AND ASSOCIATED LOW PITCH RUMBLE NOISE, SEEMED TO CHANGE WITH THROTTLE CHANGES. NOISE LASTED UNTIL TOUCHDOWN. RUMBLE COULD NOT BE HEARD ON TAXI IN. INSPECTED AIRFRAME AND BOTH ENGINES, RAN ENGINES AT ALL POWER SETTINGS, ALL ENGINE PERAMETERS IN LIMITS AND MATCH EACH OTHER. NO RUMBLE OR VIBRATION DETECTED AT THIS TIME IAW MM 71-00-00.