I'm not sure if this was brought to the attention of the Zorin team, and it could just be a one-off issue but I couldn't really find it anywhere else. When using media controls for audio levels while in-game (specifically OW2) it drops the frame rate of the game when the audio level overlay appears to indicate the change.
Specifically this seems to happen when using the mouse keys on my Razer Naga Pro which has a few keys set to media controls such as volume up/volume down and mute. When using the keyboard, it is ok.
Hopefully there's a fix for this, but I thought it could be brought to the team's attention in case this issue is happening on other games.