I have a 2004 Avalanche Z66 that I got in Jan. 04. It just hit the 36,000 mile mark. I have taken it to the dealer 7 times for this problem. I finally filed a claim with the BBB against GM. They have slotted the crossmember, greased fittings, greased the intermediate steering shaft, and a couple of times said the problem needs to get worse. When they greased the steering shaft, this fixed another problem that was felt more through the steering than the actual popping noise in the front left. The problem still exists.