I just bought a 08 350Z GT, the vibration is noticable above 40mph. Feels like tire balance. I can feel this vibration throughout the car. Steering wheel is steady and when driving and I let off the gas the vibration increases for a second then decreases with speed. Had the rears balanced with the Hunter 9700. Dealer claims 25 lbs. is the limit and both are at this. Going to have fronts done as well. Any thoughts? could it be drive line, ie U joints? Thanks for all thoughts. BTW car only has 687 miles on it and dealer mechs can't feel the vibrations claim it is road and low profiles, I don't agree with this as my 07 with same Rays Alloys and tires didn't do this.

 

UPDATE, left front tire was out of round. New tire from dealer and car is smooth as silk.