Squeak

May be the brake pad wear sensor beginning to hit your brake rotor, some brake pads come with a thin metal tab that hits the rotor and make a chirping sound warning you that your brake pads need replacement

I have same car that had the same problem when I was idled at a stop light,etc...It turned out that a small bolt to the muffler hanger that secured the hanger against the chasis somehow vibrated loose. The problem was cured after the bolt was tightened/replaced--hope this helps :)