Had the same problems with my '07 X3. First, the yellow BRAKE and 4x4 lights came on about 50% of the time, car drove fine, no noises.
Battery was about 5 1/2 years old, black light was on, replaced battery.
Lights still came on, however the car drove fine, no grinding noise.
After about 3 weeks the red Air bag light came on one morning in addition to the other two lights. Took the car the the dealer, they traced it to the ignition switch. Replaced switch, picked-up the car today, no MILs so far, will update if anything changes. $450.00....ouch.