I had a post on here a lil while about a whining or a high pitch noise when I take off when my truck is cold. Anyways it happens mostly in first gear and usually goes away when you get out of first or are a little into second gear. My uncle is a mechanic at a Chevrolet dealer here in town and he informed me that it was the carrier bearing in between our drive shafts. He spent like 2 days trying to find exactly what was causing it on a customers Xtreme and finally found it to be the carrier bearing. I am having mine replaced on Tuesday. So if you are having the same problem, you might want to get it checked out.