Footsteps sound when camera is moving

Hi Babylonians!

Anybody knows how can I detect when the camera is moving so I can play a .wav of footsteps?

I use this snippet to play audio:

var pasos = new BABYLON.Sound("Pasos", "audios/pasos.wav", scene, null, { loop: true, autoplay: false, volume: 5 }); 

and works fine but I want play it only when camera is moving.

Just in case, I´m using a FreeCamera (w,a,s,d).

Thanks and regards.