Hurumph in the right rear wheel

[Jeff Gruber <jgruber@demainsoft.com>]

Dudes,
   I took my newly acquired 77 Spit to the store for tires.  (Thanks to 
those who helped me determine a good tire size.)  It now has four nice, new 
175/70s and a noise coming from the right rear wheel.  Hurumph, hurumph, 
hurumph, hurumph, hurumph, hurumph, as I drive down the road.

   And it seems to be getting worse each time.

   Keep in mind that before I bought this car, the most I knew about 
British sports cars, was that I wanted one.

   When they put the car on the lift to change the tires, the rear wheels 
drooped.  Are they supposed to do that?  When they change the tires are 
they supposed to do anything special to support the wheels or anything like 
that?

   Any ideas what the hurumph is?

Thanks.

PS  The hurumph does increase with the speed of the car, but it goes away 
when you coast with the engine disengaged.