the BBC have another interview with ben Burtt here.
He talks briefly about creating the "voice" of ET, the sounds in Wall-E and his weirdest sound:
"I remember when my wife was pregnant with our first child, I went to the doctor's office and we listened to a sonogram of the heartbeat of the unborn child and I recorded it. I wasn't thinking about the child, I was thinking, 'This is a great sound.' And I was working on a film called Invasion Of The Body Snatchers at that time and it ended up being the main sound for all the pods and pod people and all that. That was a pretty weird application but it did seem to work because it was all about birthing strange alien creatures. So it was rooted in the womb, so to speak."
He also talks about how he has managed to use some old recordings of a short wave radio set in every movie he's worked on
"In every movie I think I've got bit of my grandfather's hand radio set. I recorded some electronic sounds, tuning stations, back 40 or 50 years ago. And I have used a bit of that Morse code, that side banding, short wave sound in some form in every film I've ever done."