318 (High pitched squeal)

Today on our way home from church my engine started to give a high pitched squeal that would go away upon acceleration but come right back when I let off the throttle. I figured it was perhaps a vacuum leak but cannot find any lines that could be at fault. This is very odd and has me stumped. See if you guys can give me some input by listening to the video below.

[ame="http://www.youtube.com/watch?v=0dLzI1e7M2E"]‪VID 00022 20110717 1356‬‏ - YouTube[/ame]