What I want to do is mute the sound of the current program/window in Windows.
How I would normally go about this, is RMB on Sound Icon in taskbar (or through Control Panel -> Sound) -> Open Volume Mixer -> Find the program I want and hit the sound icon to mute it. I'm looking for a shortcut, either a system one, or a hack, or an Autohotkey script or some 3d party program that does that.