If one switches users (i.e. user one switches off, and then another users logs in) and there is sound playing on the first user, that sound will continue to play for the second user.
If the second user has admin rights, they can guess what program is causing the sound and then kill it, but that is very clumsy, and far more than what "needs" to be done.
When I open the mixer, it just shows that sound is playing. How can I stop it?
Just like processes from other users won't be shown (by default) when running task manager (taskmgr.exe) without elevated privileges... You need to run the volume mixer (sndvol.exe) as an administrator to view programs making sounds from other users.
Go to the start menu, type in sndvol; when you see it, right click on it; click run as administrator and click allow when the security box pops up, depending on your config.
[Apologies for the low quality post. I will clean up my grammar, and add pictures in a little while, just wanted to get you an answer ASAP.]
As it turns out, this is not possible. For more information see here.
