When entering or exiting bunkers (and other indoor locations), the ambient audio changes abruptly but i think it should be a gradient transition from one ambience-sound to the other.
So when you enter a bunker, you should be able to hear the wind and so on fading out, while the ventilation/machine-murmur inside bunkers should fade in and be audible from outside the bunker.
Its not the most important “bug” to fix, but it does disrupt the immersion a bit as ambient sounds in real life never start/stop abruptly just because you take another step.