It happens when I reload Firefox, having stretched the limits of my memory with dozens of open tabs.
The browser comes back up and music is playing, but I can't tell which tab is doing it. When the noise is unrecognizable, more than one is playing. Sometimes many more.
Finally, YouTube is helping us find the offending videos so we can pause or close them: A tiny version of the little triangle that we click to play a video appears in the tab of the ones that are playing right now.
From Emil Protalinski at The Next Web, YouTube adds Play icon to video page titles so you can quickly see which tabs are making noise:
The new feature, first spotted by Google System, is a very minor tweak that will be very useful for YouTube users. Because the service auto-plays content when you open a video, if you have multiple YouTube tabs it is often tedious to figure out which ones need to be paused or closed.
Below you can see three different scenarios (the active tab playing a video, a secondary tab playing a video, and both tabs playing videos) showing off the Unicode character in action:
The above screenshots are from Chrome 28, but this new feature isn't browser-specific. It worked just the same way in Internet Explorer 10 and Firefox 22.Fewer web pages have midis that autoplay these days, so this fix should take care of most of the tabs that produce a funky chorus that was never meant to be.