Since new, I have observed a vibration at the steering wheel when driving 45 - 55 mph. The dealer has determined that it is in the rear of the vehicle and appears to the driver as steering-wheel vibration. In the passenger seat it does seem to come from the rear. Dealer has checked the car three times, balanced and rotated tires, replaced tires with new ones, aligned it, but the vibration continues. I notice that it is worse in the early morning when the tires are cold. I am now suspecting rear half-shafts or maybe the drive shaft. Dealer seems baffled. Any suggestioins? Thanks, Carl