Spit. rear wheel bearings?

[Michael T Risher <risher@leland.stanford.edu>]

My T78 Spitfire makes a high-pitched whistling sound 
whenever I go more than 35 mph.  Not always, but 
certainly most of the time.  The sound seems to come
 from the rear left wheel.  I suspected the wheel bearing,
 but I could not move the wheel around at all when I
 jacked it up to check.  Any thoughts on what this 
might be?  -m