Losing sound when switching user accounts

I routinely use two different user accounts and switch between them using Fast User Switching. I've noticed that periodically, once I switch accounts, all sound output is lost. Nothing produces sound from the output port--system sounds, iTunes, streaming music, etc. Nothing that would normally create a sound gets out. I can fix this by simply switching back to the other account, where sound is output normally without my doing anything other than switching to the account. Then switch back to the first account and sound is miraculously restored there.

So there is a work-around that usually works, but this is really annoying and happens every few days. I can't figure out what would be causing me to lose sound when I switch to a user account nor how to correct this problem. I'm open to any ideas or suggestions.