After using UE 4.7.0 for more than a month, the sound is suddenly disabled and I have no idea about how to solve the problem, I’m using the Preview 7.
Thanks for your help!
It could be that it’s the same bug as in 4.7 preview 4 -> they will surely fix it with the next preview 
…or the next one … 8-}
Hence it is a preview release and should not be used for production. Your best bet is to log it as a bug as well.
Thank you so much! Hope it’s fixed soon 