there is a strange bug with gnome alsamixer on ubuntu 11.10 using gnome-shell.. the solution is quite simple..
wget http://launchpadlibrarian.net/83939881/gnome-alsamixer_0.9.7%7Ecvs.20060916.ds.1-2.1ubuntu1_amd64.deb
sudo dpkg -i gnome-alsamixer_0.9.7%7Ecvs.20060916.ds.1-2.1ubuntu1_amd64.deb