Guys I hate to say it but I've got the same issues. Ive brought mine into the local dealer where I bought it with plenty of video evidence of what was happening. The first trip in they replaced just the intermediate shaft...as that is the easiest and most cost effective attempt to fix the issue. It did nothing. I took even more video of the issues and sent them into the service manager and he advised to bring it back in once again. Naturally the tech said he could only duplicate the noise once after driving 20 miles , ( this is not straight line problem, only a turning problem). This time they replaced the steering gear and said the intermediate shaft had "frozen" up and was defective, so they kept the truck another 2 weeks and replaced these parts once again. As soon as I picked it up, the knocking and rattling was worse than ever. I can say it almost feels like theres little rocks or marbles bouncing/rolling around in the column. This is extremely apparent whenever you make slower speed turns going into a parking lot for instance. If you make a complete turn and do a circle in the parking lot, it will rattle through every rotation of the steering wheel. This to me does not sound like a knocking sound(what the intermediate shaft sounds like), but rather a low rattle as if you put marbles in a tupper ware bowl and rolled them around. ITS INFURIATING! Where in the world is the quality control!!! To top this off, if you make that same turn driving on a gravel or rock road, this problem is exacerbated tremendously. It feels also like its losing power steering sporadically throughout the turn(will jerk your hand left and right). Same thing happens turning into a parking lot for instance with a concrete lip of a couple inches. It will literally hit that, and feel as though the power steering cuts out. Its the best way I can describe it. I have forwarded this exact thread to the service manager(nice guy by the way), and he says if this many people are having issues, GM will issue a bulletin. We shall see. As of right now, I don't see it happening. My father bought the same exact truck the week after i got mine and his is having exactly the same issues. This is not all the problems either.
1. Engine light came on for whatever reason(They fixed this)
2. DEF system issues(They fixed this)
3. Hill start assist comes on for no apparent reason and completely stops the truck (at a stop sign or red light with no incline). Almost been rear ended to to the truck doing this suddenly.(They said this was normal)
4. Electronic parking brake turns on and off by itself(They said this was normal, lol)
5. Does not recognize saved or new trailers most of the time, says no trailer detected when you hook up.(They said normal)
6. XM radio always says searching for signal, lost satellite reception right in town. Have to turn off for at least an hour to reset that one.(They said GM is aware of the issue, and is working on it)
7. A/C blows very irregular . Blows strong then weak, strong then weak. No, its not on auto and am not on a call. Its as if its getting irregular voltage. Weird for sure(They said normal)
8. Android auto is essentially inoperable (They said GM is aware of this issue, and is woking on it)
9. The brake pedal half the time is depressed when I get in to start the truck( no travel left). Also has vibration type feeling while depressing it coming to a stop, or stop in go traffic.( They said normal)
10. Power steering doesn't always start working immediately . Sometimes its hard to turn right as you pull away. (They said they couldn't duplicate, naturally)
11. Brakes have been squealing since new, truck has ten thousand miles now.
12. Truck dash rattles in cold on start up.
Besides all of this, its nice and I think its a beautiful truck, . Even though my Denali lost most all the luxury features my 15 had (adjustable pedals, adjustable seatbelt strap, turn signals in side mirrors, lumbar functions in the seat, CD player (yes i still use cds), way less customization in the digital cluster, less plush steering wheel, etc., C'mon GM, DO BETTER! I truly hope they can resolve this.