I thought something had failed on youtube as the sound was gone. Restated Opera and it was back. But then i started to notice that every time i wanted to click on the youtube tab the sound went away because of this anti pattern feature.
The more tabs you have the worse the problem as the "speaker" icon covers a larger part of the area. BTW do some mouse mapping and see where people usually click on the tab to select it.
The tab must be clean with no other feature than selecting it, THEN AND ONLY THEN can you have more features on it. Basic UX common guys.