I felt so stupid today! I drove home last night, and heard this some sort of thumping coming from my car. It eas raining hard as hell so I really couldn't hear it well or even at all. I get into my CLS this afternoon, and I start driving remembering that I had heard this strange thumping sound. After I got about a mile away from my home I heard it again. So I keep driving it around a little and it kept doin it? The sound started to get a little lounder, and it almost sounded like I had a piece of wood or a nail in my tire. Finally to make a long story short I stopped by a garage near my side of town, and the mechanic took a look at it, and turns out I had forgotten to tighten one of my lug nuts down last week when I rotated my tires!!!!! Now I am a offical dumbass.