Rather than using an extension to be able to mute tabs, you can also just enable the "experimental" (I put that in quotes because it may as well be put into Chrome, I've never had it not work) tab audio mute. To do it, just go to chrome://flags and search for "Tab audio muting UI control" (Using Ctrl+F if you don't know about it) and then click enable. After a restart, what it does is add a little speaker icon to the left of the close tab X that you can click to mute the tab. It's really useful.