Alternator makes awful screeching sounds??

With a water pump problem, would I notice any change in running temperature? Sorry about the lack of info. The engine has been converted to a serpentine system, so it's a single 6 rib belt. It has a tensioner on it as well, but I'm wondering if these can loose their tension and need to be replaced. The fan is electric, so no problems there. I'm almost positive that the noise is coming from the alt area, as it's pretty far away from my water pump, but I'll double check to make sure. I put in a new alternator and it made the same noise, so I don't think it's a bad bearing. The new one I put in was a Ford part and not a remanufactured part so I don't think it's the bearings. The pulley spins freely with no belt so I'm not getting any resistance. Also, the amp meter I have on my battery is reading 12-14 volts, so I don't think it's over charging. I'm thinking it all might just boil down to a belt problem, since it's a custom set up with a custom length belt, so I think I'm going to take it to a place where they'll let me try a few belt sizes and see if that fixes it. Any ideas before I take it in to check are great though, as I'd love to save the time and expense by fixing it myself. Thanks for all the suggestions so far, keep them coming.

Update: So I took it to a shop and had them give me a second opinion. The belt is slipping on the alternator, which is making the screeching sounds. Soo... why is it slipping is my new problem. The tensioner was a little sticky, so we lubed it up but that didn't seem to effect anything. Unplugged the alt (I know, not supposed to do this) and the noise went away, so it seems like the alternator is tougher to spin then it should be when under load. So, any ideas about the alt? After driving for about 10 minutes, the alternator was super hot, so I feel like it's overcharging. It's a 3G alternator. Anyone have a link to what voltage I should be seeing at the connectors? I searched but couldn't find anything. Any help is as always very appreciated.

It's reading right at about 13.5 volts. I'm wondering what the voltage for the connections are supposed to be. There is a wire that tells the alt when to turn on and I'm wondering if it has the proper voltage. Also, is there any way to tell if a tensioner has gone bad?