This script installs a big MUTE button in your toolbar/menu to toggle the active attribute of the Sound Track.
Therefore enabling you to mute and unmute the Sound in 3D Studio MAX.
It registers a callback to sync its state with opened files and reseting 3D Studio.
This updated version (2) now has the missing callbacks.
Install this Macroscript by evalutating it.
You will find it in the 'rdg::preset' category of Customize -> Customize User Interface.
It is called 'enables/disables sound playback'.