My 05 ZX3 has started to make a groan when I'm doing a 3-point-turn or when driving slowly through a parking lot or something. There is a slight vibration that can be felt through the steering wheel. The groan happens whether I turn left or right. What's weird is sometimes it'll do it allot, and then go weeks without doing it. I've checked the power steering fluid and it's topped off, looks kinda black though. Any ideas? The car has 33k miles.