Loud whirling fan noise...

[kthankzbye]

I did a search on this and I can't find a solution to this.
I was driving back one day and a loud fan whirling noise came on. It sounded like the fan was on super high speed. I turned off the car and started back up, it took only a second before the loud fan sound came on again. I waited 2 days without driving it and it's still there. It's really loud that I'm afraid to drive it down the street.
I opened the hood and It's coming from the fan I think.
I'm not sure what to do, should I call BMW assist and have the car towed. Driving it would be embarrassing cause it sounds like it's about to blow.
Thanks, much help needed.