I've noticed that even when I kill all the sounds within FSX such as the Cockpit, Environment, ATC, etc, that the APU noise still emits from within the cockpit on the default Boeing 747 & CRJ's, it does not do this with the 737 however and I can mute all the sounds using the sliders.
Any idea why this sound is imposssible to MUTE?
Thanks
Trainee
Chief Captain