My friend has an '85 280SL, and the doors close with a vault-like "thud"; no vibration or rattling, just "thud". It sounds like the doors weigh 500lbs each (hmmm, actually they just might), and this is a convertible. It definitely gives you a feeling of security and safety. The doors on my '71 Triumph TR-6, by contrast, close with a "slap k-k-k-k-dang-g-g-g-g", which inspires a feeling that the car is made of balsa wood and bird saliva, which it probably is not. As much as I love the TR (a car most Benz owners just would not understand), the sound of those Benz doors closing just screams "quality" to all who are in earshot.
Colin