I don't have any problem making the planes whistle. The problem is matching it to airspeed, because the engine sound needs to reduce in volume just right for you to hear the whistle from the cockpit just like it works in real life (except our canopy is always closed, also). Nearly every airplane whistles, including the big bombers. The real problem comes in with making planes whistle with the engines off, which they do in real life. In AH they won't, because everything is tied to the engine on event (the engine being on). It would take a change in programming for that to work. I'd like to see it because it would get around a huge headache with vehicle tracks, too.