I have A 2013 Countryman S ALL4.
Recently it has developed a noise when under acceleration, I’ve replaced the tensioner, no luck. It only happens when I press on the gas, once I let off of it the noise goes away. Only happens when driving, not when parked and reving
It sounds like wind howling... not sure it that makes sense. Hopefully someone can help.

 

Try to post a audio clip, hard to diagnose without hearing it.

 

My brother in law is a transmission mechanic, so I took My car to him and he found the problem. My transfer case went, not the greatest time trying to find a replacement, but I was Able to and he installed it. Sounds perfect now

 

What other problems did you notice while you were hearing the howling? Any other symptoms?