There is a self answer here http://superuser.com/questions/783277/how-can-i-keep-audio-in-windows-8-1-from-fading-in-when-i-start-playing-a-sound#comment1018963_783277

The OP states 

> I asked this as a guest but when I answered the email to set up the account it seperated somehow so I don't know how to get back to that guest account again (glitch in the guest-to-user algorhythm).

 Not sure if it is a bug or not?