Oh. My. God. Did anyone have to watch this thing in school? I had to...in the middle of the late eighties, at the height of the "satanic panic" in rock and roll ("What's happening to our children??!!??"). Apparently, it's still around! In fact, it's become sooo popular a "sequel" has been made. Here's a great article about it from Pitchfork:
Watch out for that evil Satanic backmasking!!!
Hell's Bells doc
Ba-DUMP
Videos