My '03 RCSB does the same thing. It's really annoying. I have only 9700 miles on it and it's made these poping noises every since it had about 1,000 on it. It's getting worse. Unless I'm on baby-butt smooth pavement, it makes the noises as soon as it starts rolling. It does it going straight and is no worse when turning. I can't isolate it to one area of the front. Seems to be coming from more than one place, so I don't thinks it's the steering colum problem that seems to be fairly common. I've pushed down on the front end a few times with it in my garage, and don't hear anything, but I need some one else to do that while I'm under it.

If I ever get my notice from the dealer to bring it in for the tailgate cable replacement, I'll tell them about the noise, but since my dealer kept my truck for three days just to balance the worthless American General tires that came on it, I'm not inclined to take it in for service unless it's for a serious problem.