hello, my car makes this very high pitch sound, yet low volume, when im driving at low speed, around 20-40 mph. it is hard to hear when i'm outside, but when i'm driving in enclosed parking lots, it's much easier to hear. the sound goes away when i step on the brakes, but it starts up again as soon as i press my foot on the accelerator. does anyone have any idea what this might be? my car is an '03 325i with about 65k miles...