If the you only hear the sound when you are braking, it sounds like your brakes are bad. I would check them. As far as a ball joint, it can make a noise, but it won't be a scraping noise. I've heard clunks, creaks, and even a squeak when the steering was turned, but never a scraping. Please check your brake shoes (rear) and brake pads (front).
Let me know if this helps and what you find.
Tuesday, October 21st, 2008 AT 1:33 PM