With the recent updates to GMod, facepunch has added a few pretty sweet features, one of which ill cover in this suggestion. Its clientside voice scale. Typically you are stuck with 2 options when it comes to people who are being relatively loud on the server. You have option A - mute them, which if they are giving pretty good callouts as to who the traitors are wouldnt be ideal even if they are being loud. You have option B - Lower the voice scale of the whole server, which could make it to where the soft spoken are harder to hear.
Now we have a third option. With this new update each player could have their voice scale increased or decreased with how loud or quiet they are being. https://gmod.facepunch.com/blog/june-2021-update This is the link to the recent update showcasing the features added. It explains that the code is default on the sandbox scoreboard by default, but for other gamemodes it will have to be implemented by either the gamemode developer or the server developers manually. Luckily I have found said code needed to make this a possibility.
wiki.facepunch.com
Not only does this work on a per player basis this also works on a per server basis. Say you turn a player down for being too loud, the server dies down and you eventually make your way to vanilla. If said player also hops to vanilla, the value set on one server will be persistent when you both hop, as long as you dont close your game between servers.
Now we have a third option. With this new update each player could have their voice scale increased or decreased with how loud or quiet they are being. https://gmod.facepunch.com/blog/june-2021-update This is the link to the recent update showcasing the features added. It explains that the code is default on the sandbox scoreboard by default, but for other gamemodes it will have to be implemented by either the gamemode developer or the server developers manually. Luckily I have found said code needed to make this a possibility.
Player:SetVoiceVolumeScale
Sets the voice volume scale for given player on client. This value will persist from server to server, but will be reset when the game is shut down. This doesn't work on bots, their scale will always be 1.

Not only does this work on a per player basis this also works on a per server basis. Say you turn a player down for being too loud, the server dies down and you eventually make your way to vanilla. If said player also hops to vanilla, the value set on one server will be persistent when you both hop, as long as you dont close your game between servers.