migrated from scifi.stackexchange.com Aug 12 '12 at 21:13
I just listened to it in the show lead-in on the Hanna-Barbera section of Warner Brothers, Turner website. To me, it sounds like a metal gym whistle being blown with a finger covering part of the opening. Back in my lifeguard days, I played a lot with my nice chrome-plated whistle, from loud to almost no sound at all.
Okay, facebook wouldn't let me upload an audio clip and I didn't have anywhere else to post one so here's a link to a video I had to produce - just so you folks can enjoy (heh) the sound track.
Enjoy the sound track.
My guess is that it is the sound of the magnetic field generated by an electric motor, that is turned into an electrical signal by an inductive transducer (similar to the pickups on an electric guitar), recorded on magnetic tape, and played back at variable speed.
Some years ago, I put a inductive pickup (that was sold by Radio Shack to record telephone calls via "listening" to the handset speaker) on a hard drive and recorded it spinning up and powering down, and it made some really cool sounds. A variable speed cordless drill also sounded very sci-fi.