First off you'll need to open up vent and click the little button next to the Bindings dropdown.

Next, hit the New button to create a new Bind.

The next step is simple, name your Bind.

Once you have named your bind, select it from the dropdown menu and hit Add.

Here you will set up the function and hotkey for the Bind you're adding, so click on Toggle Mute Sound, then click on the hotkey box and select the hotkey you want to use, mine is set up for the combination of LCtrl+LAlt. Once you've done that hit OK to exit out of this screen.

Here you'll see the bind all set up, just hit OK again to exit out of the Bindings setup.

Now all you have to do is select the binding you want to use from the dropdown and it will be active.

I found this very handy while questing as it allowed me to turn vent off with a simple hotkey if I was in a cinematic, and still allowed me to be hanging out with everyone while playing.