I was driving down I-215 today, when suddenly everyone in front of me came to a stop driving about 65-70 mph. I a few people darted into other lanes to avoid a collision. I used my BMW brakes to stop my X5 quickly and without a problem. However, after the fact, I noticed that my brakes were squealing a bit when I stopped at red lights. I went home let my rotors cool down for about 30 min. Lter I went back out, and now everytime I come to a complete stop my brakes squeal. I also noticed a dark line going around the top of the rotor on all four of my brakes. I am thinking this is just brake dust, not sure?? Suggestions are greatly appreciated. Thanks in advance.