They obviously tweet the living lights out of an original sound (could have been something so basic as a 404), or it took them/him no longer than 20 seconds to tweet. It all has to do with sound skills and sometimes simple luck of finding a nice sound quickly by accident. It happens!
Then, they used a vocoder and probably some final last moment edits on the entire recording for smooth sound. That's it.
My two cent!









Checkout this Interview of Ben Burtt on Wall-e:
http://www.youtube.com/watch?v=A58fMkMo3cM
Have you seen the movie?
What did you think of the sound?