i had the same issue with my truck (2004 ext z71). my guess is that your driver side bearing is out, or going. i ordered a new one off of ebay for $115 and installed it my self in about 4 hours. now my truck isn't 4x4 so im sure that helped the process be a little quicker, however while i was changing the bearing i went ahead and changed my front brakes, rotors and pads, which i suggest because more than likely if your bearing going out, it will put excess preasure on your pads and rotors, as it did mine. any how hear are the pros to the DIY process.
project cost was a lot less than taking to a repair shop.
the after market bearing i bought ( click here
to see it, i found the exact company and part that i ordered) has some issue responding to the ABS. so although my truck runs fine now and im having no more issues, my computer reads abs traction fault.
that is my only complaint, but im sure if would have ordered the part direct from gm this issue would not have occured.
any how two repair shops quoted me 425 and 455 to fix it, so in roughly 4 hours, $115 bucks for the bearing and how much ever the rotors and pads cost at advanced, sorry cant recall, i saved my self around 200 bucks