Gmod Left Ctrl Mute???

So this just started happening recently. Whenever I crouch on Gmod (left ctrl) it mutes my computer sounds. When pressed again it unmutes it. Is my keyboard broken or something? None of my addons change or add keys except for F menus (F1,F2, etc.)
I’m running windows 7 64 bit.

Does it only happen when you’re in Gmod?