My vehicle is at the dealer (going on day 7) to correct a vibration problem (along with a heater fan motor --- really cold drive to the dealer at 7* with no heat or DEFROST....). Mine vibration, however appears to be drive shaft or transmission related because the frequency is higher than the wheel speed rotation rate.

Most noticable at 30-40 mph and worse when cold so I am guessing it is probably a u-joint or similar, though they haven't figured it out yet. I will post when the figure it out.