I need some help! I get this horrible vibration in the rear of my 79 280ZX everytime I go above 45mph. All the wheels are balanced and the transmission is new. Could it be the rear end?? The vibration used to start when I would deaccelerate at speeds above 60 then it moved to 55 then to 50 now is vibrates all the time after 45. Doesnt matter if I am accelerating or deaccelerating.