At varies times while driving the tailend will shimmy, vibrate and feel like I am riding on rough terrain.

Last spring brakes front were vibrating - dealer replaces brakes and rotars front and back. Since then, front brakes have vibrated off and on - upon inspection, after 1000 miles, they replaced pads and brakes again. Rear brakes have continued to squeak since last year. upon inspection last week, front brakes are "dark", "wearing quickly" again (less than 1000 miles) and rear brakes are "glassy" which they say is causing the squeak.