The problem with my Ubuntu 12.04 LTS system is that it seems like something other than me is controlling volume and mute status of my sounds. Whenever a sound is playing, the volume icon in the bar goes between normal and mute icon about 10 times a second, and the sound I hear is according. And when I adjust the volume either with the keyboard buttons or with the slider that comes from the said volume icon, it seems like something is trying to put it back to where it was. It seems like everything's ok when the volume level is below 25 %, so I was thinking maybe some kind of "automatic volume level setting" could be behind this, but I haven't seen anywhere an option to turn such a service on.
The problem appears in Gnome and also when no X is running. In the latter case, when I run alsamixer in the console, the volume bars jump between mute and unmute there as well (but only while a sound is playing).
pacmd list-clients |grep application.name application.name = "ConsoleKit Session /org/freedesktop/ConsoleKit/Session2" application.name = "GNOME Volume Control Media Keys" application.name = "Indicator Sound" application.name = "XSMP Session on gnome-session as 1013c4e19cf8151dec138928909599998800000018450036" application.name = "Metacity" application.name = "libcanberra" application.name = "ALSA plug-in [mpg123.bin]" application.name = "UNIX socket client"
mpg123 is there because I was trying to play something while taking that list. Other than mpg123, the list is identical when no sound is playing.
Stopping, killing or uninstalling pulseaudio did not fix it.
One more thing: the OS is located at an external hard drive which I don't use every day. I think the problem appeared suddenly one day, maybe as a result of routine package updates?