I have had an annoying rattle in my 300E since I purchased it 6 years ago. It seemed to come from the front and only happened when I hit a sharp bump at low speeds. It was a very solid clunk sound that I could not seem to isolate in the garage. A post about the impact strip on the rear
bumper comming loose got me to thinking that might be the problem so I removed the bumper only to find the impact strip was properly attached but the foam blocks inside the bumper assembly have
dried out and shrunk enough that they can move
about when a sharp bump is hit. I used RTV to
attach them to the bumper cover and my rattle is now gone.