Comment 17 for bug 162701

This bug is also related to pulseaudio. You can demonstrate this by killing pulseaudio, which makes all applications that use sound work normal again. It's quite sad to see no progress on making pulseaudio handle this kind of situations. See somehow related bugs #226692, #230837.

Next time you encounter the bug try following:
$ pidof pulseaudio
6163
$ kill -9 6163
...and to restart pulseaudio type Alt+F2 ... pulseudio

It's an ugly workaround, but it works at least for me.