I have no idea what is going on but my sound settings now no longer work properly in 15.04. I firstly upgraded to 14.04 and then to 15.04. Before I had sound control buttons on the very top status bar, they are no gone. And, the auto-mute used to work when I plugged in my headphones before, now that no longer works either. And to top it all off, the sound settings GUI in System settings is opaque which means I cannot see it properly. What is going wrong here people?!! Not happy with THIS upgrade at all.
its a permission issue, it happened with me as well. on ubuntu 14.04. open terminal and run
sudo rm -r ~/.config/pulse
and force reload alsa
sudo alsa force-reload
it should be fixed now.