SoundBreak is a free utility that performs one simple task: It mutes the sound whenever a user locks his/her session.
The default behavior in Windows is to keep playing whatever sound the user was playing, which can be quite annoying if other users need to use the same computer. SoundBreak fixes this problem.
It's extremely simple to set up: Just download the installer file and install it. No configurable options, no complex setup, it's just a simple install.