try this, rotate the tires from front to the rear, if the vibration stays the same, the shocks may not have the proper amount of pressure in them causing an over rebound, thus getting your vobration. if the vibration goes away, have someone drive in another car near you and watch your rear tires to see if they "bounce" while driving. if they do, the problem is the tire, and if you contact the manufacturer, let them know the problem, they will replace them for free. Its the law and if they do not replace them, you can contact your local BAR Bureau of Automotive Repair office and file a report. then contact the manufacturer and let them know that you have filed a report with the BAR for selling you a faulty safety related item on your vehicle. tell them that if they fix the problem for you, you will drop the complaint. do the same thing with the shocks if they turn out to be the problem and the dealer doesnt do anything to help you...