While you are right about the check6 sound, the problem is you either have to include a copy of the same sound with every aircraft or vehicle, or you get the same sound. It's also possible to make an air raid sound that isn't irritating, but we also have the ability to turn it down if we need to. Right now the air raid is only read from the sound folder, and will not be picked up if you change it for a particular airplane, or vehicle. It would add a lot of depth to the game if you choose a German plane and everything like the air raid siren, check 6, and gun sounds (defensive) become typical of "your" air raid, check 6, and guns.