By default Unreal Engine mutes games when alt tabbing, but I dislike silence so I looked into how to fix it. Super simple fix.
Go to:
C:\Users\<YourName>\AppData\Local\FarFarWest\Saved\Config\Windows\Engine.ini
and then add:
[Audio] UnfocusedVolumeMultiplier=1.0
then save.
You also need to make the file read-only as Unreal will overwrite it on startup.
right click the Engine.ini file > Properties > click read only
