It's really annoying when one of your browser tabs is making noise and you can't tell which. Lately, sites have been using an informal convention of showing a play indicator (▶) in the tab title. It's a simple solution that really helps out your users.
You can try this out live on the Herding Code site.
Super Simple Approach That Mostly Works
The super simple way to do this, which would cover most cases, is to watch the pause, ended and play events and toggle the document title.
The problem here is that it doesn't work well if you've got more than one audio element on the page: start two playing, pause one, and the play indicator goes away even though one of them is still playing.
Still Pretty Simple Approach That Actually Works
This just watches for a change in state on any audio element on the page, then checks to see if any of them are playing. If any of them are playing (not paused) it sets the play indicator and exits out since there's no need to keep checking. That's it.
Note: If you're using Wordpress 2.6, just grab that chunk of code and add it to the footer of your site inside a script tag.
Slightly More Details
You might think that iterating elements to check for something in jQuery is a bit daft, but that's the best I (and my Twitter friends) could come up with. I've used attribute selectors in the past, and was kind of hoping there was a way to select on properties as well. Something like this:
Other Notes Of Interest To People Who Like Notes
Note: you could also do the same thing with HTML5 video elements, too. They've got a paused property as well.
Note: If you're using a plugin like Flash or Silverlight, it'll take you a bit more work, but I think your users will appreciate it - in Silverlight you'd use the Silverlight HTML Bridge (example); in Flash it looks like you'd use ExternalInterface (example).
Note: Yes, I punked you by setting the title of this post to include a play indicator. It's the new RickRoll. ▶ on ▶er