I have bed crackling in rear speakers, had it in for service, "nothing wrong with the BMW parts!" so i sent it back to the guys who did the phone kit (THB Bury) he came down took out the head unit, disconnected everything apart from the factory parts... still crackling and actually go off altogether intermittently. so rang BMW back and going in again... beginning to be annoying!
only bought the car in May so still under used warranty.. i'll update as i go.