Our 2004 Mercedes C240 developed this vibration problem some months age. From a cold start there is significant vibration (wobble) of the steering wheel for the first five miles or so. Then it fades away. The dealer has changed tires and wheels, has balanced and rebalanced, and has replaced the motor mounts--all to no avail. Warming the engine up before moving does not help. There is no vibration at all when the car is not moving. Any suggestions?