Hi, digester here so I can't really respond in a normal reply fashion, but..

Check on the alignment of your alternator and it's pulley.  If the mounting
bolt(s) or brackets are a bit worn, the alternator can be out of line with
the belt and "Jill-poked" as the belt passes causing it to squeal.  Just an
idea, if you haven't already looked at that.
  Don Hanson