Belt squeal associated with something like this isn't constant, it usually only squeals when one part of the belt makes contact with a pulley. Like when coolant gets on a belt sometimes you'll hear a squeak, then a pause, and then a squeak once again when that one slick part of the belt comes in contact again.
This actually sounds like a needle bearing on the idler going out. The ones that typically tends to go out is the grooved one on the very front under the coil packs, 8 in the picture, or also 9.
