Immediately afterwards I got a metal-to-metal grinding noise whenever I turned the wheel. I swapped the 15s for 16s, and the sound is still there, albeit less frequently. Mostly from the front driver's side.
Sometimes when braking, I also get an awful grinding noise... usually as I approach a stop on less-than-smooth roads.
That's usually a sign of worn out pads. If the scratch is not deep enough, the rotors can be
resurfaced. Jack the car up and spin the wheel.
Do you hear a metal to metal noise the the wheel doesn't spin freely? If so, there may be some foreign material lodged in between the pad and the rotor - or some clip came out and is stuck in between them.
If no noise, then maybe that foreign material had been chewed away
else if, the pads are worn
Either way, you need to have your brakes worked on. I can't remember if it is stamped on the AUdi rotors, but most rotors have a minimum thickness in millimeters as a guide for the brake guy turning the rotors. He'll know if he has to grind too much material and you'll need to get new ones. Recently midas charged us $20 to turn 2 rotors. I used to do it when I worked in a shop.