I've had an issue with the truck for a while now and I've been to the dealership several times but it keeps happening. The first time it occurred, I was driving the truck and there was a vibration in the steering column. I also heard a knocking noise. I was told at the dealership that the shaft went out so they had it replaced. The same thing occurred several times after that. The truck was repaired. However, on one occasion while I was driving, I heard the knocking noise again. Once again I went to the dealer who claimed that the shaft went out. Do you have any idea what keeps making the shaft wear out? Is there maybe something else causing the vibration and noise?
Without hearing or experiencing the noise myself, it is hard to make an accurately diagnose this but GM has a TSB (technical service bulletin) that may address this concern. There are 3 possible causes from a body mount at the A-pillar, to the frame, to possibly the intermediate shaft just failing. The body mount and frame tend to make the noise when the body flexes. Not sure if either of these are the problem but a set of chassis ears while duplicating the noise would lead to the proper component. You may want to enlist the help of a mechanic, such as one from YourMechanic, who will have the tools and equipment to diagnose and repair the clunking noise.