I have a 06 S430 4matic with 19,000 miles on it. When I bought the car new, it had been a left over and had been sitting in the showroom for a while. When I did the test drive there was a vibration somewhere in the car, felt like a bent rim. They told us that it was because the tires had flat spots from sitting and it would go away. It didnt. They ended up replacing the tires for me at 1500 miles. I felt like the problem went away but it is now seemingly getting worse. They told me it needed to have the tires balanced again so I let them and it is still there. After that they said they couldnt feel it and didnt know what I was talking about and all mercedes ride like that. I took my uncle for a ride in it who has owned many mercedes and he told me something is definately wrong as well. Any thoughts? He told me there are sometimes drivetrain issues with the 4matics.

 

it could be the long shaft area where the rubber mountings are damaged ... ive come across to this before.. do check em.. its a possibility engine mounting damaged...vibration to chassis...

if it vibrates to your steering wheel that's a sign showing something wrong with your tires,rims or wheel balancing or center rim rings

 

Was this car a demo? How many miles was on it when you bought it? I bet they know about it and that is why it was in the showroom and left over! Any good bodyshop should be able to diagnose it and find out what part is damaged/needs replacement.