John, first be sure that all of your door seals and window seals are in good
order.  These can make some racket if they are bad.  Next you could try
pulling all the interior panels and insulating the van with fiberglass
insulation.  That is what VW did on the later model Westies and
Wolfsburg/Carat Vanagons.  My Carat was really quiet until the driver's side
window seal went bad.  I just got a new one and hope that the noise level will
go back down to whisper mode.
Ken Wilford
Van-Again
John 3:16