What's wrong with my car steering system?

I have a 1998 Mercury Sable GS, with about 127000 miles on it and it used to be a rental car. Now it's mine I got it in late 1997. These days (and granted these days the weather goes from freezing to warm in this state, MA), when I turn my steering wheel (I have 2 front tires that are still young)when I'm not in motion, I hear a dry squealing sound up front. But when I'm moving at least 4 or 6 miles per hour or faster, I never hear this sound. I've had my fluid check ok. Albeit some station I know does claim a steering fluid leak but my friend the mech. denies it. What do you think it is? Should I take it to my mechanic friend?