On which tab is playing sound, if you get the Opera extension, "Download Chrome Extension" you can download then extensions from the Chrome store, and install them in Opera. Of course, use your Opera browser to go to the Chrome store and download, and then go to your menu, extensions to install it.
I think the Chrome extension, mute tab, ought to be able to help you.
Here are reviews of it.
This may not be a perfect fix for you, but I hope this might help, and keep you with Opera 🙂