I am familiar with the SLK 32 site that has the same article as you describe. I've had the exact same noise since my car was new, but I haven't heard it for awhile now. I almost forgot about it until you brought it up.

The noise sounds like a loud thud, or pop, which only occurs while sitting still with the engine running. I thought about taking it to the dealer, but decided against it after having the transmission and rear end changed and almost everything else in between worked on. After my last bout with them and the hassle I got in getting my seat cover installed properly, I've finally realized when it comes to this car and Chrysler, some things are best left alone. I did not want them tearing up the bulkhead and all the trim behind the seats to fix a problem that happens only infrequently.

I don't think anyone here has addressed the issue with a Chrysler dealer. Can you imagine the BS you'd run into trying to get it fixed? It seems to me that the Crossfire has been all but abandoned by the dealerships who are starting to breath a sigh of relief as warranties started to expire this past June.