Combine the new computeSpectrum of the SoundMixer class with some water ripple effect
Turn on your speaker. The larger the value computeSpectrum returns, the more the ripples e.g. when the song goes silent, there will be less ripples.
Song: Last War by Jay (3.9MB mp3 loaded dynamically into swf)
Update: Download the source here. Let me know if you still encounter any errors