I've been told there is a bearing or bushing of sorts on top of the front spring / strut tower that binds up. It manefests as a clunk with wheels turned and backing out of say a driveway or parking space, usualy a downward slope. It starts as a clunk and will progess to a "boing" as if the sring has sprung. The bushing or bearing binds as it rotates. I thought it was a broken spring but my suspesion guy tells me its common in full size GMs. Have yet to replace, haven't driven the Bonnie much. She'* become a bit of a Garage Queen these days! He said remove the cap shoot some oil down there to quiet for a while, eventually a $300 replacement to do.

Pretty sure it is the strut mount for my GXP. I had it up on the hoist last night, and everything seemed nice and tight. No play at all in the stabilizer/sway bars. Since I'm creeping up on 100,000 miles I might just replace the struts and the mounts just for good measure.

BTW..... Good call Burgh Thing!

I put new struts in along with mounts, the ride quality is now better. It is much firmer! I also went ahead and replaced the stabilizer links with Moog Heavy Duty links, and am glad I did. Both links were very rusty, barely anything holding it together! I cut them out with a sawzall and replaced them. Easy enough and no clunk!

wow, that'* a tough one. maybe check the lug nuts.. good luck