2006 BMW 325 Fan running very loud when heater is on..

I noticed my fan was making a loud noise when my heater is on. It gets really loud and goes up than down and up and down. Sometimes it won't go off. Sounds like an airplane running. Then today when I was driving it the hot air turned to cold and the temperature light flashed on and the car overheated. It only makes the loud noise when the heater is on. Any suggestions would be appreciated. Thanks!