Popping sound [Resolved]

Mid-June we started hearing a popping sound when we turned. At first it was only when we turned left after slowing down just enough to turn into the neighborhood. Then it appeared on right turns as well. Since it is still under warranty (but barely at 33,500 miles) we took it in. The dealer said he installed shims to stop the noise. At first this seemed to work. Then about three weeks later the noise is back and this time it is worse. I was wondering if anyone out there has experienced a similar problem. I thought that maybe if I went to the dealer with a little more knowledge then maybe I could get it fixed before it is out of factory avalanche warranty.