I'm not sure how helpful this will be, but I have discovered I only have the sound issues when I don't have any mods installed. I installed the community a4 and the Hercules mod which weirdly fixed the sound issues. As soon as I uninstalled them the issues came back.
I also noticed when I had these mods installed, some of the textures were missing on some of the liveries- mainly only the wing textures.
I have no idea how having these mods would affect the mirage sound, but that is my experience.
EDIT- just did some testing and can confirm it is the community A4 that fixes the mirage sound when it is installed in my case. I uninstalled/ reinstalled it multiple times, and each time it was installed, the mirage sound was fine, and each time it was uninstalled, the mirage sound was broken. Maybe this would explain why some people have the issues and others don't?