I have had my TC for less than a week. Been noticing some short, sharp, very loud knocks coming from the rear whenever I back out of my garage, and as I am rolling slowly over my gravel drive. It will have a typical pattern like - Knock...Knock Knock.........Knock. After I get onto pavement the knocks seem to stop. I thought maybe it was my tires throwing stones up against the chassis, or maybe the spare was not hanging tightly in the well, but it seems tight. Can't find anything loose in either of the rear interior service panels. It also seems that shortly after I start to move there is a single (related?) knock that sounds like a loud version of an auto door locking function that locks doors after reaching a certain speed. This happens as I am backing out slowly. These knocks don't sound isolated underneath. They resonate through the body quite loudly. Anyone experience this one? Thanks.