Slight vibrations at the drivers seat!

[Forestville]

A new commer to the H2 World and lovin it, however, my 2005 has presented a very slight vibration felt through the steering wheel and seat at certain speeds. Initially occurs when I hit about 52mph and tapers off, but never completly gone at 55 with less and less felt the faster I go. Ive had the front wheels aligned when new BFG's were just recently installed, new U-joints on the rear drive shaft did cure some of the vibrations (mechanic said they were very stiff), but I can still feel it. Any idea's or similiar expeirences?