I just bought a 2001 Suburban that was doing this and after reading a couple of these threads I decided to try a short cut. I took out the lower bolt (under the hood), retracted the ISS toward the firewall and sprayed some WD-40 up into the shaft splines using the little red extension tube. I cycled the shaft five or six times by hand and then re-assembled. That was two weeks ago and my noise is gone with no return. I figure a can of WD-40 is about three bucks so I can buy about 30 cans for the price of one steering shaft. May not work for everyone, but it' s the best 2 minutes I ever put into a car.