It's possible that the brake wear sensor is loose. That happened to me and I just had to get a new one installed. The best option is to take it to the dealer (or a trusted BMW tech) and have them check it out. We're only speculating. When it comes to the safety of your car, it's best to have it looked at by a pro so you know for sure. Then decide what to do once you have the facts.
2008 Monaco Blue/Tan interior 335i sedan. Mods: AFE intake w/ scoops, AFE Exhaust, ER FMIC, Koni FSD/Eibcach Pro-Kit, Breyton Race GTS wheels w/ Continental ExtremeContact DW tires, Cusco OS strut bar. BavAuto Black/Beige seat covers w/ black floor mats, M3 rep trunk lip, eBay front splitters.