Anyone know how I can mute a game when I minimize it to do something else like search the web?

I recently got a new Lenovo Y Gaming Headset (it's a usb one) but I realized that now for some reason whenever I temporarily minimize a running game, I can still hear the game's sound in the background (when i'm on the desktop main screen). This hasn't happened before so im assuming its the headset. Any help is appreciated.

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