For some time now I have been experiencing a strange phenomenon on my laptop: at odd times it has suddenly started playing music. It would always be the same music – some kind of instrumental which I could not place. The strange thing was that it was playing more than one copy of the musics at the same time, generating a strange cacophony.

I worked out that it would only happen when Firefox was open – something which I was able to verify by using the Volume Mixer when it was happening.

I searched on the web thinking that it must have happened to someone else but no luck.

I finally worked out what was causing it and I thought I would share it.

I stalled a Firefox extension called “Distil Web Monitor” and I configured it to watch a particular web page for changes (I was waiting for their 2016 price-list to be released).

I was monitoring 3 versions of the page (in 3 different languages).

Each version of the page includes a video. This video is normally muted by default. Here is the HTML which is used to embed the video:

<video autoplay="autoplay" muted="muted" loop="loop" poster="videohome/COMMERCIAL_SHORT-G.jpg" style="width:100%" title="">
		<source src="videohome/COMMERCIAL_SHORT-G.m4v" type="video/mp4" />
		<source src="videohome/COMMERCIAL_SHORT-G.webm" type="video/webm" />
		<object type="application/x-shockwave-flash" data="videohome/flashfox.swf" width="164" height="92" style="position:relative;">
		<param name="movie" value="videohome/flashfox.swf" />
		<param name="allowFullScreen" value="true" />
		<param name="flashVars" value="autoplay=true&amp;controls=true&amp;fullScreenEnabled=true&amp;posterOnEnd=true&amp;loop=false&amp;poster=videohome/COMMERCIAL_SHORT-G.jpg&amp;src=COMMERCIAL_SHORT-G.m4v" />
		 <embed src="videohome/flashfox.swf" width="164" height="92" style="position:relative;"  flashVars="autoplay=true&amp;controls=true&amp;fullScreenEnabled=true&amp;posterOnEnd=true&amp;loop=false&amp;poster=videohome/COMMERCIAL_SHORT-G.jpg&amp;src=COMMERCIAL_SHORT-G.m4v"	allowFullScreen="true" wmode="transparent" type="application/x-shockwave-flash" pluginspage="http://www.adobe.com/go/getflashplayer_en" />
		<img alt="COMMERCIAL SHORT-G" src="videohome/COMMERCIAL_SHORT-G.jpg" style="position:absolute;left:0;" width="100%" title="Video playback is not supported by your browser" />
		</object>
		</video>

So what must have been happening was that, at regular (but seemingly mysterious) intervals, the extension was going out to fetch the 3 pages to look for changes and, when this happened, all three versions of the video started to play but they were not muted!

So I removed the 3 pages from my Distill extension (the new price-list is out now) and the problem has gone away.