I have a 2001 Saturn SL2 that is having a problem with one of its headlights. When I turn on the headlights, frequently one is not lighting. If I go to the front and give the lens a quick knock, it turns on and stays on until I turn the headlights off. It doesn't flicker or show signs of a loose connection. I have cleaned the connector and that hasn't helped. I'm out of ideas at this point and hope someone can suggest a next step.