Hello again gang,
the sound has gone away.  So I can't experiment to find conditions to make
it come again ... but now here's a real stumper ...
Although I'm not the kind who takes drugs I'd swear that when I drive my
vanagon through snow (which is falling rapidly) that around 25-30 mph,
the world takes on a different sence.  Instead of me driving on the road,
the road is going under me while I am standing still.  This same 
sensation hits my wife also ... and almost at the same speed.
Has anyone else noticed this ?  It is not something I have ever noticed with
another vehicle.  For those that have noticed this, what do you do to
return your concentration to reality?
Perhaps it is just that the vanagon runs so smoothly at 30 mph.  Perhaps
it's too much propane.  Who knows?
Stuart Hutton (hutton@poly.oscs.montana.edu) 1982 diesel vanagon camper