Have you looked here? http://www.need2speed.web.com/

Dean has a nice site with a lot of 500E/E500 related data, maybe we can convince him to start a registry??

I cannot help with the "cluncking" sound as I have not heard of this on a 500E before. Has the car ever been damaged in the rear before?

Benzmac may have a clue with some more vehicle history maybe??