i just put 4.10 rear end gears in my mustang in over drive about 70 to about 120 it vibrates the back lash is set at 8 thousands i did see that there is a spot on the drive shaft back towards the rear end there is a spot on the drive shaft about 1 to 2 inches wide like there is somthing rubbing it when im driving around town no noise or anything just up around 70 and up it vibrates a little and when you put your foot on the gas a little bit there is a little howl before i put the cover back on the rear end i spun the axle no binding or catching the gears were spinning free and smooth