I switched from Ubuntu 11.04 amd64 gnome2 to 12.04.1 with mate-desktop-environment.

Generally sound still works as it should, but only if I don't mute it. Once it's muted I can't re-enable it. I have no idea what to do except buying another sound card...
But maybe someone has an idea what to try instead of changing hardware?

josef@josef-ubuntu:~$ aplay -l
**** Liste der Hardware-Geräte (PLAYBACK) ****
Karte 0: SB [HDA ATI SB], Gerät 0: ALC662 rev1 Analog [ALC662 rev1 Analog]
Sub-Geräte: 1/1
Sub-Gerät #0: subdevice #0