I own a 2000 Taurus sedan and the steering wheel pulsates at high speeds. It starts at about 50MPH and continues up to about 75MPH. I've balanced the tires and got the brakes inspected. Could it be that the tires are cupped and need to be replaced or is there a chance that one of the rims is warped. Would a wheel warp cause that much pulsation simply from going over rough bumps or potholes?