Just would like to know how others solved the problem with this since if you hit anything above 70 miles an hour 105 kilometers an hour. It is the most annoying whistle that you have ever heard with it on the autostrada.

 

While not specifically discussing the ski/snowboard rack there have been a few threads about noisy roof rack systems. Try this one or this one.

 

On the stock MINI roof rack bars I stuffed the open ends of the cross-bars with foam rubber (underneath the black locking covers). No more whistling for me.
Also, double check that you have the cross-bars placed per MINI's instructions. I'm sure you realize there is a front and a rear bar and they're not interchangeable...and their orientation to the car is specific as well.
Try the foam rubber in the tubes. That's where your noise is being generated.

 

Thanks I will try filling that space with something, thanks for the heads up on the right placement lucky for me it came with pictures so I got the bars in the right place. Did you also try one of the air dams or anything or just the rubber in the ends

 

Thule provide some form of rubber strip that slots into the gap with their bars.
I'm going to try that (have some left over from previous bars) this winter.

Of course with stereo cranked up and 2 kids in the back i'd be lucky to hear any whistling at all

 

I had some bad whistling with the factory rack only with out my cargo box on it. i pulled the rubber strips out and no more whistle. The rubber I am talking about the one that goes the whole length to cover the inside mounting tunnel. No more whistle for me! It is easy to pull them out, and easy to put back in if needed.