Now this particular truck has 340K miles on it so things don't go so smoothly as I would hope. The reason this truck made so much noise while driving was that the top of the shock was really loose. This caused the shock to go up and down causing the threaded portion of the shock shaft to file away at the steel shock mount.
Have a look below and you can see that instead of a round hole for the shock there is almost a figure 8 shape from the shock filing it's way through the steel.