- Be sure the correct Sound card is selected in GSX. Exit from the sim and restart when you apply the changes.
- Be sure your audio card supports OpenAL, which is required by GSX (and many other games too). This depends on the audio drivers. Sometimes, it's best to use the sound drivers that comes with the card, sometimes the opposite, and the ones provided with Windows works better. There's no general rule, you must just try different solutions.