and he indicated the noise was always from improper install. The gears are all pre-tested and the tolerances for each gear set are stamped on the gears. He recommended finding an installer who was "old school" who could fabricate shims to get the tolerances exactly right. Found the right installer who was comfortable "fabricating shims" and had them installed (replaced bearings seals etc. as well).. Mine are just as quiet as stock...and they do bring the car to life. Love em. (Mine were NOT the first batch).