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