Alternator Noise??

if the bearings are on the way out, they can make noise. you can get a mechanic's stethoscope and check it out. you can also use a long screwdriver. in any case, be very careful - dont hit anything that is moving or hot (fan blades, accessories, etc) with the scope/screwdriver or your body.

good luck.

If the rectifier (diode pack) inside the alternator goes bad it can make an electrical humming sound.

After I fitted my UDP set I also got a noise from the alternator, but it was more of a rattle. I dont know if its the same as yours? Any way, it turned out it was the nut holding the alt pulley on which kept working loose. You are supposed to put them on with an impact driver but since I dont have one I used thread lock and as much torque as I could manage. That solved the problem.

Check the nut is tight on the alternator pulley.

Also squealing noise is a common problem when the belt gets loose. Check that the tensioner is operating in the correct range. If not then you might need a new and/or shorter pulley.

Best of luck.