Sounds like your problem is 2 fold.
1- vibration while driving. From your description it sounds like you have a tire out of round or cord seperation. Although you don't have that many miles on the tires, I've had new tires off the shelf go bad in just a couple weeks. It's rare, but it does happen.
2- Vibration on braking. This could also be caused by a tire, but most common cause is warped brake rotors. Hope this helps.
Monday, December 15th, 2008 AT 3:14 PM