[Vwdiesel] 81 Rabbit - wheel balance issue

[rbp at 4u2bu.org]

hey gang - I have something going on in the front end of my 81 Rabbit
sounds and feels like an unbalanced front tire
but I put new tries on front recently, balanced, and there was no sign  
of this for the first month or two
AND, it goes away when I am turning right
gets worse turning left
so obviously not a tire
it's a thumping sound directly coordinated w/ tire RPMs
going slow it's thump-thump-thump, @ highway speeds it sounds like a  
gatling gun
(OK, not that loud, but you can hear and feel it)
wheel hubs are not warm to touch after long highway driving
any thoughts on what this is?
thanks
Rolf in MA