Mike,
Apparently the problem is the "X-Plane 11\Output\Preferences" folder, must be corrupt for some reason.
I removed the entire file, saved it in a temp folder on the desktop, and launched the game again to auto-create a new "Preferences" folder > Sounds are working fine!
Once you launch again, your x plane program, will start up with the original learning tutorial at the beginning of install, but no files are lost anywhere in the program.
Worked fine for me.
Mikey H (P3regrine)