That volume slider graphic thing kind of disappeared. I'm not talking about the volume icon in the system tray, but the one that quickly flashes in and out when you press the volume control keys on your keyboard. Interestingly, sometimes, very rarely though, it does show up, but most of the times it doesn't. And I don't know what is causing this erratic behaviour. Can this be fixed?
Here's what I'm talking about (this is not mine, just a picture I pulled off the Web):
PS: I'm using the Gnome Classic desktop environment in Ubuntu 14.04 LTS.