ORIGINAL: HI Hoe
Sounds like your intermediate steering shaft needs lubricating. Check with your dealer; they sell a kit for that ($20, or so). There was a TSB on this issue also that requests the dealer replace the shaft. If it's still under warranty, get them to do it.
I have an 04 Avalanche which is making the same noise. It makes a clunking type noise when turning or when hitting bumps. You can feel it in the steering wheel. I have checked the front end for any "play" and the ball joints seem fine. I think it may be the steering shaft.
My truck is no longer under warranty. Can anyone tell me how to lubricate the intermediate steering shaft. Is this the shaft that runs between the firewall and the power steering box??? I would like to fix this myself if possible. Thanks.