We recently took our Mercedes to Virginia Auto Service for  a new set of tires. Since we purchased the vehicle there has been a vibration in the rear of the vehicle. We have taken it to several places, including the dealer, to have it repaired, to no avail. When Matt balanced the tires on his new machine, that simulated road force, the problem totally dissapeared. I guess it pays to go to the shops with the most high tech equipment. thanks guys!