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:
Long clip of helicopter flying in, landing, and taking off again. I left a lot before and after so you can fade it in and out as much as you want. Used iZotope RX5 to remove loud bird sounds during the main portion of the helicopter sound.