I often get a noise that sounds more like snapping or cracking than creaking. It comes at random times, but it seems to me to be most associated with sudden movements of the body, as when entering or exiting a sharp corner or doing rapid acceleration or deceleration. I hear it as coming from either overhead or behind my driver's seat. Sometimes I think maybe it's the body frame flexing around the sunroof hole, other times I've thought maybe it was one of the seat belt buckles slapping against the body - but I have never been able to pin down just exactly what it is. I get it pretty much at least once every time I drive the car. The first time I heard it was on the drive home from picking the car up at the dealer and it freaked me out totally. I've gotten accustomed to it by now, but I do still wonder what the heck causes it!