My best guess is that your computer is outputting 5.1 (or similar) sound while connected to stereo speakers or headphones.
The fact that G4 is working as expected may seem to disprove this hypothesis, but I wonder if there's some other difference that could account for that. Do some sound drivers allow per-application profiles/settings these days? I honestly don't know. Regardless, I believe this avenue is worth exploring.
Can you tell me more about your setup?
- What kind of speakers are you using?
- Are they plugged directly into your sound card? Into your computer's front panel?
- When kind of cables are you using? Are you perhaps getting audio via HDMI or S/PDIF, for example?
- Are any other components (e.g., an A/V receiver) involved?
- Is there anything uncommon about your setup?
Try this test:
- Load a 3D airport.
- Load a model with an internal combustion engine that will produce sound even when idling. If you want, you can give it a small amount of throttle to make it louder, but make sure it's still low enough that the vehicle remains stationary.
- Use the WASD keys to walk near your aircraft.
- At this point, you should be able to look around in any direction using the mouse (do not click!).
- Pan around the scene. Does the audio for your aircraft come in and out depending on the direction you're looking? For example, does it fade out when you're looking at your aircraft, but fade in when it is to your right?
This may sound silly, but is it possible the sound is just too quiet for you to hear? I expect it to be loudest in cockpit view and when the aircraft is near you in other views, and full throttle is louder than idle, naturally. These are exactly the times you say you can hear things. Is the audio quite loud at those times, or merely audible but on the quiet side?
At the times when you cannot hear your aircraft, are other sounds affected? Try holding down Page Up to crank up the wind. Do you hear it? Try mousing over the left side of your screen, then hovering over the different Gadget Tabs. Do you hear beeps as you move from one to the next?
As 12oclockhigh suggested, ensuring your sound drivers are up to date is a good idea.
If you attach your system info here (please do not include serial numbers), I'll take a look at it and see if anything jumps out at me.
I realize I've asked a lot of questions here. Please be thorough in your response and answer all of them.