Yeah, the P51's famous wind howl that she makes has certainly captured my imagination and this sound was something that the Nazi and Japanese forces feared the most during the War. It's defenetly there, it's loud as well....it's been captured on camera by amateur video recorders. Like you mentioned in the reply above, it's no 100% certain of it's cause...good cause here of course. My biggest theory about it which makes alot of sense is due to heavy air ram being pushed through inside the big scoop underneath in the middle of the aircraft. Due to the the custom design of this scoop around the sharp finish at the edge causing the melodic howl when the mustang is at high enough speeds. I think the gun holes have no relation to the wind howl.
In general my understanding of wind howl in general is that the movement of air sets things vibrating which makes noise, but I don't know the specifics. For example, if the wind is blowing hard, you can often hear the wind howling at a certain pitch in this case the mustang's high speeds. This seems to be dependent on velocity because the harder the wind blows, the higher the pitch is. If you stand behind a house whilst the wind is blowing from behind you, if the wind blows strong enough you can hear it while it's hitting the edges sharp corners of the house. I guess it's all about physics and human ear, noise is the result of vibrations in the air which excite the ear drums at those frequencies to which the ear is sensitive. I guess the howling sound of the P51 is a big part of the aircraft, I belive this the most perfect re-creation of the P51. Probably you'd also be morelikely to hear the P-51 howling if there is bit of wind blowing up there as well. I had no idea that not all mustangs have it which defenetly makes me scratch my head
I'd kind of hope that further research would made towards this howl in contiuation....the P51 with howl will defenetly complete it