Car shakes. My '05 Cobalt starts to shake on the interstate after driving for a little while. When i hit the brake, it starts to shake real bad until i stop. I put it in park or turn the steering wheel left then right and its fine again until i drive for a little while. The power steering alert comes on every now and then, but it goes off if i turn the car off and then back on. I hear a rattle or a knock when i make sharp turns at low speeds.