I have a 97 Mercury Tracer. Last week the steering wheel started shaking a little. It is getting progressively worse. It doesn't matter what speed I am going, it still shakes. The faster I go the harder it shakes. If I go very slow it jerks at each rotation of the tire. Any idea on what this could be? I have been ripped off in the past from mechanics because I am a girl and I want to be able to know somewhat about what the problem could be before I take it in.