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:
Evening choir of black cap warbler, blackbird, robin, great tit, crows, upflying flock of wood pigeons, and hammering of a woodpecker in a forest near Cologne, April 2006. Vivanco EM35, Marantz PMD671