I have a 2003 Ford Focus ZX5 that I just bought a few months ago, and I notice when I accelerate through a turn, the steering wheel jiggles and the whole car gently shakes. But when I'm taking a turn and not using the gas, it's smooth and normal. I also notice when braking hard from high speeds the steering wheel does the same jiggly thing, not to the point of losing control, but enough to get your attention. What's wrong with my car?