If the grooves in all the grooved pulleys are clean , you might have to give back the belt if the noise goes away when sprayed with water.

Have any of the components the belt drives been replaced? If there is an alignment problem it could contribute to belt noise.

 

I took off the belt to inspect things this weekend. I have not replaced anything in this system (except the belt last year). I can't see anything wrong. I spun everything that I could spin and checked for side-ways movement, but nothing obvious. I did try and clean everything, thinking road grease/oil could be having a negative effect. It quieted everything down a lot. Unfortunately, it is very hard to get into that tight area and do a good cleaning!

 

Some other possibilities: Tensioner pulley bearing, alternator bearing, A/C compressor pulley bearing. The alternator bearings are known to "chirp" when they are worn.