Hi
Before we start: I am no expert on sound systems. So if someone else is, he will probably give you a better answer. For the time being:

It would help to be a little more specific: does the problem appear when you move the throttle, or whenever throttle is open? Second, what (sound)hardware are you running etc.

I had a similar problem once which turned out to be a bad connection after I installed a headphone. Removing the extra connections solved the problem.

Also I had some problems with my sound before I downloaded the latest drivers.
Finally, when I again encountered problems I decided to ditch the "sound onboard" an installed a decent soundcard.
Still, when for example ATIS messages appear (the green line in top of the screen) sound goes bad. I turn them off when possible.

In a nutshell:
check connections, remove any you don't really need;
download drivers;
upgrade or live with it until a pro helps you out.

Hope it helps
AJ

I'm afraid I can't help you out here. Seems to me though that your system just may not be up to the task.
Sound seems to be very heavy on the processer so I think it's a lost case.
You could try to set all or some display settings to minimum, maybe that would help. Also set sound to minimal (in the game, press alt then "options". Go to "settings", choose "display" and/or "sound" to achieve this)

Cheers
AJ