In fact, I don't have either one of those services on my CentOS box. I do have two tools, gnome-volume-control and gnome-volume-control-applet. I believe the second of these is the app that actually displays the icon in the tray. Running it manually doesn't solve the problem though. I suspect I have to somehow reload the kernel driver controlling my sound, but I'm not sure just what driver is being used. Seems to be a lot of sound related modules.
Oh well, time to reboot again...