Comment 8 for bug 335201

The fun you're having with volume keys/knobs sounds familiar, but is a different bug.

What happens for you, is that the kernel sends a volume change notification in the form of a key press, and gnome-settings-daemon interprets that key as a request to change the volume, triggering another notification from the kernel in an infinite loop. Changing the volume key bindings in GNOME preferences might be simple a workaround.

What happens for me (and what this bug is about), is that sometimes when I'm pressing various modifier keys (Ctrl, Alt, Shift), gnome-settings-daemon grabs the X keyboard and doesn't release the grab. Its likely this is related to the "show mouse position when you press Ctrl" setting that I have enabled. Volume keys don't enter the picture.