The vanagon has large sections of sheet metal that, effectively, act as
a drum. This is because VW didnt' put any sound deadening material on
them. This includes, the front doors, the sliding door, the side panel
opposite the sliding door. The addition of a small amount of deadening
material to these will result in a substantial reduction in road noise
penetrating into the cabin.

While the engine DOES produce a fair amount of noise, at least in my
Syncros, VW did put a little bit of deadening material on the deck
above the engine.