I had the same problem with the front tires on my '85 until I (mumble
mumble) rotated them... They had developed a strange diagonal wear pattern -
high spots  in left tire looking like  "/" and high spots in right tire
looking like "\".  The van also sounded like it had a worn out wheel
bearing, but when I checked the individual tires, I couldn't find the
problem.  Then somebody on the list suggested rotating - which I hadn't done
in a very, very long time, because the front and rear tires were purchased
at different times and I left the better tread on the front, as my dad had
once advised me...  Three thousand miles later, the noise has gone away and
the old wear patterns have vanished.  Before I buy new tires this year I'll
make sure a real mechanic checks the front end - I have around 200K on this
bus and haven't replaced anything up there since I bought it with 105K on
the odometer.  I'll also have the alignment checked by a good shop.  Then
I'll rotate the tires, honest.

Randy, Carla & Anna Huyck, Olympia, WA
'75 Rustfalia
'85 Vanagon GL
'90 Fox GL