On GotSound.org we are using wavesurfer.js to play sounds in a browser.
It's works only in modern browsers supporting Web Audio.
MediaElement fallback to support old browsers like Internet Explorer not always works.
You can find more information about browser supported Web Audio API here.
Please, consider to upgrade your browes to one of the following:
various noises taken while having fun with balloons. recorded with a sony MD, then re-recorded on my comp using ableton live and a m-audio usb quattro soundcard. then sliced in audacity.