Disabling the sound plugin probably won't fix it, as it is the media-keys plugin that is using Pulseaudio. (The sound plugin uses it too, but not all the time). gnome-settings-daemon now uses Pulseaudio for setting volume (in exactly the same way that gnome-volume-control-applet does), so if you disable Pulseaudio, your volume keys won't change your audio volume.
Disabling the sound plugin probably won't fix it, as it is the media-keys plugin that is using Pulseaudio. (The sound plugin uses it too, but not all the time). gnome-settings- daemon now uses Pulseaudio for setting volume (in exactly the same way that gnome-volume- control- applet does), so if you disable Pulseaudio, your volume keys won't change your audio volume.