Squeak sound from belt

[cashville]

I got a noise on idle, and specially on acceleration that is coming from the belt (i've tried a method which is using a candle wax on the belt, the noise went away for a minute but it came back, so I know for sure it's coming from the belt or some part related)
Before replacing the serpentine belt, I would like to try other methods to see if i can remove the noise, because the belt doesn't seem that worn out. Maybe the noise is coming from the pulleys.. Anyway I can isolate the noise with some tests, so I know the right parts to order?