[rmutchler]

Mine was doing the same thing, specifically when I would put in gear and turn hard left, or hard right...popping noise most of the time. Was normally one pop, then again when I turned the other direction. Took it to the dealer today and it had to do with the cross-member, and there's a bulletin out on it 03-08-62-002I. You can google the bulletin number for more info...it fixed mine. Here's a bit from the bulletin:

Document ID: 2006229 #03-08-61-002I: Snap/Popping Type Noise Coming From Front of Vehicle (Remove Bolt-In Front Crossmember and Add Washers) - (Aug 27, 2007)

Subject:Snap/Popping Type Noise Coming from Front of Vehicle (Remove Bolt-In Front Crossmember and Add Washers)

Models:2003-2006 Cadillac Escalade2003-2006 Chevrolet Avalanche, Suburban, Tahoe2004-2007 Chevrolet Silverado (Classic)2003-2006 GMC Yukon, Yukon XL2004-2007 GMC Sierra (Classic)2003-2008 HUMMER H21500 Series (½ Ton) and 2500 Series (¾ Ton) with Two-Wheel Drive

Condition
Some customers may comment on a snap or popping-type noise coming from the front of the vehicle. This condition is most apparent during hard left or right turns at low speeds. Going over bumps while turning may also aid in producing this noise.