Is there anyway to inject or add APU sound to aircraft? Even most of my payware aircraft have APU sounds but I can never here them. It should be faint in the pit and loud outside. But even outside I can never here them start up, run or shutdown. Is there a known issue with sound? Any help would be appreciated.

As far as I know, the APU depends on the ability of the add-on developer. Not all aircraft will model an APU, and even if they do, most of the time it's just a cosmetic addition to the aircraft. Some of the CLS/JustFlight jets come to mind for me: the APU doesn't actually do anything, but you can hear it when it's on. So FSX should be able to support APU audio, but how it does that I don't know. Aaron Swindle would, though. Jeff ShylukSenior Staff ReviewerAVSIM

As far as I know, the APU depends on the ability of the add-on developer. Not all aircraft will model an APU, and even if they do, most of the time it's just a cosmetic addition to the aircraft. Some of the CLS/JustFlight jets come to mind for me: the APU doesn't actually do anything, but you can hear it when it's on. So FSX should be able to support APU audio, but how it does that I don't know. Aaron Swindle would, though. Jeff ShylukSenior Staff ReviewerAVSIM

Well I remember some add ons that I applied third party sounds to that exchanged the sound cfg with a new one and they worked great. That was mostly in FS2004 but it really takes away from the realism part, for me anyways. I hearing APUs all day long at KDTW.