Now it's back, but instead of being white, it's red. (I checked everything I could think of, enabling the notification, checking all the boxes in the control panel and in the realtek control panel, making sure it wasn't a 'hidden' icon, etc.) I would restart the computer, and it would be back, but then later disappear. One minute it's there, and then Poof! it's gone. I noticed that recently the little speaker icon for the Realtek HD Audio Manager (on the taskbar next to the clock) seems to completely disappear at times.