I KNOW I KNOW
Its your warning pin on your brake pads. When they get low, a medal pin sticks out a little and just rubs against the disc letting you know to change your pads. When you brake, the pad pushes down and you cant hear the pin. Just change your pads and you'll be set to go. Ive heard this on almost all of my cars and its a good and easy fix. >

>
Also, It'll only get worse as your pads wear further and further down... making the sounds louder and louder as the days pass... change them before the pin begins to make grooves in your discs.