whistling during acceleration with AC on

[hambone1983]

Folks, I am still new with my 2006 X5 4.4i - and been noticing that while driving on the road, about 40~50 mph and above, there is a whistling noise from the front, this only happens with the ac on. If i turn the ac off, the noise goes away within 10 seconds. If i let off the gas pedal, the noise goes away, so its tied somehow to the acceleration + AC on.

I've cleaned the ducts for any blockage, leaves, etc. The cabin air filter is clean too. All hoses look good and the the serpentine belts have been replaced.

This only happens with the ac on and when off, its a quiet ride. Any ideas? thanks.