I'm pretty sure this has been asked many times before, but I can't find any similar threads atm.
Anyway, this is completely possible with a plugin. It's not client-side.
I don't feel like writing and testing code right now, so try hooking teamplay_broadcast_audio or something like that.
Check out this similar plugin:
https://forums.alliedmods.net/showthread.php?t=167713
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