This computer lacks working sound, but I’m going to go ahead and assume this mysterious sound you refer to was the sound of him landing on a giant marshmallow.
I prefer to think he then climbed up the cliff and flew again and again, regardless of whether it ruins half the message!
How bizarre. I just happened to notice this last night as well. If I remember correctly, it was some guy’s masters thesis. The sounds seemed a little off, but I didn’t know if that was because of YouTube or because that’s how it was done.
I first saw this a couple of months ago. Here’s the guy’s thread on its debut at CGTalk. You may need to log in to see images, but I think teh text and video links will work okay.