Not really much in the middle of the truck. Even the steering shaft really would not make a sound in the middle. I have never seen a steering shaft that was not felt through the wheel but that does not mean that that it is not possible. I would definitely look into the possibility. Here is a thought of some thing that would come from the middle just a little father back. The drive shaft could be getting stuck in the back of the trans. This would happen over bumps, stopping and going. It would also be worse when colder and sometime when raining . To fix it would be free and maybe worth trying to see what happens. Un bolt the drive shaft and pull it out of the trans. Put grease (lots) inside the shaft where it slides on/in the trans. If it goes away it will be temporary but then you can get some good grease and do it again. I usually use 2 tubes of the grease the dealer sells for the steering shaft.