Happened to my wife's A3, too! We turned into our street and out of nowhere a nasty grinding noise started up. A 1/4" pebble happened to pop up and into the gap between the shroud and the disk. I was so happy that I was in the car when it happened because I never would have figured out what it was if she had just come home and said those horrible 7 words, "My car is making a funny noise."

Anyway Etlsport, I'd be surprised if that's what's happened to you, because her A3 made that sound constantly - not intermittently. It probably is some dirt or debris that got caught somewhere under there. Start with a bottom-blaster car wash and/or a power washer in the suspension, brakes, etc. Clean her out good and see if that helps.

Good luck!