We have an '07 Mercedes 320 CDI, and it is by far as smooth as the 350 gasoline version - I've driven both.
You truly
have to listen for the diesel sound of the 320 CDI at idle to hear any perceptible noise. The turbo whistle is by far the loudest sound from the engine.
If presented with the V6 gas or diesel version of the Mercedes, hands down the diesel version trumps the gas. Particularly with torque and fuel economy. The power is just wicked...
