I keep experiencing intermittent shaking of the steering in my Saab 9-5 Estate. The wheel shakes and shifts, but not consistently. It feels like a flat front tyre and the brakes also shake. It comes and goes and is not speed related. Fluids all seem okay and the garage can't figure out what's wrong as it keeps going away. I can stop the shaking but it requires stopping and turning the steering from extreme left to far right a few times.