I have a 2000 Ford Expedition XLT that vibrates at all speeds. At first i thought it was a wheel out of balance. I took the vehicle to Belle Tire and had 2 new tires put on and the other 2 removed and re-balanced. This did not do the trick. The vibration seems to be originating from the rear of the vehicle. The front end alignment seems to be fine since the steering wheel does not shake or vibrate. Anyone have any ideas what this might be?