Hi Silfarion,
Sorry to hear about your troubles with the sound

I know you said you've tried all the recommended fixes but I just wanted to let you know what the current list of "things to try" with crackly sound looks like:
1) Go to the sound settings and move the sliders on to cause a quick volume reset.
2) Make sure you have the latest drivers for your sound card
3) Make sure you don't have something strange running in the background (youtube always causes problems for me).
4) Turn bloom off if you have it on. Try turning down your graphics settings.
5) Open your user settings file (in the Settings directory of the game install directory) and set SoundUseHardware to TRUE.
6) Go to your Sound and Audio Device Properties in control panel then to the Audio tab and go to the advanced Sound playback and on the Performance tab set Hardware acceleration to standard.
7) Check if the problem still exists in windowed mode (video settings)
Most of the problems people have had with the sound have been resolved with one of these. The static sound is usually a result of the game not being able to get sound data to your sound card fast enough for some reason - often because the amount of data it is pushing to the video card is hogging the system bus, so turning down your graphics settings can help alot.
Failing that, could you post the name of your Asus board?
Thanks