You might try this thread.
steering wheel knock
That said, I tried the sleeve fix (the moveable sleeve in the engine bay) described in that thread and it didn't work. I put it back to it's original position just in case.
I can duplicate the sound by shaking the u-joint on the steering shaft down near the brake pedal. As nearly as I can tell, the sound and feel is simply the shaft bumping against the sleeve that surrounds it. My truck sees a ton of miles off-pavement and I've noticed this sound and feel for a very long time with no change. I'm comfortable now that nothing damaging is taking place and am ignoring it until something convinces me otherwise.