I have a 1990 Synchro Westie.  During the last month it has developed a 
loud, low hum and strong vibrations.  They get worse with higher 
speeds, but seem worst between 40-50 mph, and above 70mph.  Engine rpm 
does not affect.  They are also getting worse/louder with time as I 
have not been able to locate and fix the problem.  Distinct, strong 
vibrations are transmitted to the entire van, but seem especially acute 
in the stickshift arm.  Moving the arm to certain positions seems to 
quiet and change vibrations a little.

I suspect, in order, the viscous coupling, driveshaft, rear 
differential, and transmission.  Cursory check of (rear) bearings and 
CV joints seem fine.  Any experience or suggestions?

Richard Lee at pcpros1@ix.netcom.com