@sheisbrooklyn it happens to me even when only one tab is open (netflix)

Yes, me too. A youtube video sound started playing while i was registering on this forum to respond xD. For me, Everything you've mentionned is also true for me, but for one exception/a detail to clarify ; The videos's sound start playing even if there is no youtube tab currently open.
Generally the problem bothers me when i'm watching Netflix, and the sound goes away when i click on another tab, or after waiting for a bit. I hope they fix this.