Speaker icon missing from systray in Windows 7 SP1

One day, shortly after installing Windows 7 SP1, I realized my volume icon was missing from the system tray. I tried all the fixes I could find online: some didn't work at all, some worked temporarily. The volume icon would re-appear and it would 'stay' there for the next 1-2 reboots, then it would be gone again. These solutions involve messing with the registry, checking all you Windows settings and so on.

The fix comes from Microsoft itself: MicrosoftFixit50229.msi. Download the file and run it, it worked for me.

The problem is not the same for everyone, but I do think you should try Microsoft's solution before going through the registry without any experience.