So I got my lumia 930 a week ago. And it's quite perfect so far. But there's one HUGE problem with WP - notification sounds go mute (don't know why or how) until restart. After restart they work for some time, and then they go mute again. Then new restart and so on... anyone got ideas? I know it's not so hard to restart a phone, but doing so few times a day? And missing calls because - phone doesn't scratch a sound...
the answer could be to Uninstall Lync2013 app.
Goto Setting-> Notifications + actions there you will find
for more information see this link
Make sure your volume is up the whole way, and Quiet Hours is not turned on. Otherwise you could try resetting your phone. If that still doesn't fix it, you may have a defective device.