steering problem please help

Hey felllas, on my 2000 Z71 I have a problem. Mostly when I am in a reverse backing in to a parking spot at a very slow speed and I have the steering wheel cranked to one side is when it happens. There is a big thump... it sound like when you shift from first to third... like the transmittion is trying to grab the next gear. it also happens sometimes when i am in drive, but mostly in reverse when i am turning to steering wheel from the far right or left to the center. It happens about halfway through. It is very hard to explain, I hope someone out there has some idea. any help would be appreciated.

Do you feel it in the steering wheel? If so, it is probably the intermediate steering shaft.

//2000CAYukon

I feel the reprocussion in the steering wheel.