Sound bug solution ?
 

I also suffered from the sound bug in MP.
After app. 5 Min. in game, the engine sound starts to stutter, one minute later the sound died completly. :-x

Now I turned off the voices in the audio options and the enginesound stayed the complete online session.

What do you think...

Certainly one to try.

Well spotted!

I tried this. It worked well for a few sorties but then I still got the garbled sound and then had it cut out for a bit.