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:
rain and several thunder claps. Stereo. Recorded with a minidisc recorder and an AT822 mic. Edited in Protools and saved as a 48/16 wav file. I have more sounds available here: http://sfx.TakomaMedia.com