i had the same problem, front suspension arms were broken. chevy replaced under warranty but now my cambers are bent and the chevy dealer is trying to sell it off as an alignment issue. fight with them, take it back every single day til it is fixed right. make it seem like you have nothing better to do then bug them to fix it. they'll either eventually get tired of you or they'll hire someone competent enough to actually test drive the vehicle long enough to hear the noise. also, one thing they offer out here is to have a mechanic go on a ride along. that would be something else to try.