I have a 1999 Ford Contour and when I turn the AC or the heater on, my car idles really loud and shakes even if I turn the AC and heater off after it starts making the noise. If I turn it off, turn off the car, and restart it, the noise is gone. Sometimes if I drive the car for an hour it starts making the noise. Does anyone know what it might be? It's never done before now and I really want to figure out what's wrong with it because I love that car.