You shouldn't feel any metal to metal type vibration if the motor mounts are installed correctly.
The following list is to confirm you have all of the right parts for the rear mounts. There is an Upper Rubber Mount (U-shaped), a Lower Rubber Mount (small rectangle that fits up inside the cross member), a Spacer, a Lock plate and the Bolt.
The lock plate gives the bolt a larger surface area to press against and locks the bolt from turning. If you just use a split ring lock washer there's not much keeping the bolt from being pulling up through the Lower Rubber Mount when the truck frame twists or there is heavy engine torque.
Mike B
