If you have a habit of locking your system a lot then this utility called Mute on Lock is especially for you. This utility disables the sound that comes from the speakers when we lock our system.

Mute on Lock is a tiny resident utility that sits in the system tray and monitors your session: when you are locking your Windows workstation, it mutes the sound of your speakers. Using this tool you can mute or unmute your speakers when locking the computer.
You can either double click the tray icon or use an optional hot key as a shortcut for the same. The tool is small in size and free to use.
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