If the sliding window is a littlebit open, that would make a difference. You can hear the noise from the window, but its no interference with the noise reduction system, its just the sound of the passing of the air caused by the slot. But as soon as its closed, its ok pretty quit. But still if you move the head close to the window, one can hear the air passing by on the outside. I havent tried full open yet, during flight, for some reason. only during taxi due to exessive heat in cocpit on warm days. But then there is no interference, just a difference in the noise level.
The passive noise reduction is not good at all. So make sure you always have spare batteries with you.
best reg.