my brake light has been on for about half a month now. i couldn't figure it out. i looked at the passenger side rotor (through the wheel), and i notice on the outer edge on the rotor there is 3 grooves cut into it, they are aprox. 2mm deep. the driver side is fine. i look in and saw that i still have a lot of brake pad left. i couldn't get the wheel off (damn shop torqued the bolts down too much). any advices on what these grooves could have come from?