[urq] More quattro news, HELP

[Andrew S Basinski]

So I was under the impression that crazy electronics was only a part of 
British cars...but several of my problems seem to have corrected 
themselves, and my wiper motor is blown...i just swapped the one from 
the rear to the front.

Big problem.  My car develops heavy shaking at about 45-55 mph 
sometimes.  Not all the time, just on occasion.  It seems to be the 
same time my vacuum check valve is making noise.  Does that make sense 
to anyone?  My tires seem ok, no flats spots but they may need 
balancing.    But why would it only happen sometimes?  Seriously, 
sometimes it's fine, other times it scares the heck out of me.  What 
could be doing it?  The previous owner said he had an alignment done 
before I got it.  The car has new shocks and new wheel bearings, as far 
as I know.  Why, on earth, does it feel like the wheels are falling off 
sometimes?

-Andrew