Throughout my time playing Gmod I had to deal with bad mics, squeakers, and toxic people. You can mute these people through the tab option in some servers but I was never fast enough. By the time they were muted I had already suffered severe brain damage. Now I am sharing this solution with people. I am a little late and sorry for the many of you who had to endure this.

To mute these types of people simply open up console and type

1) bind "key" "voice_scale 0" to mute all mics
2) bind "key" "voice_scale 1" to unmute all mics

For example:
bind "m" "voice_scale 0" will mute people when you press the m key.
bind "n" "voice_scale 1" will unmute people when you press the n key.

This is useful so you can quickly mute the player before you use the tab option to mute them in game. It makes the process of muting a particular player less painful.