I have seen this listed on several forums - I have a 1994 Sable with 194,000 miles and recently had a serpentine belt squeak which I dived into because I could not get it to stop. Ford Dealer said it was my water pump. HOWEVER I went simple first - thank god for "lifetime" repair parts from AutoZone! I changed the guild pulley, the belt, then the belt tensioner, water pump, power steering and finally the alternator and NOTHING WORKED stilled had a high pitched squeak. (Note I did find a small water leak and while you are near water pump ALWAYS change out the 4" of hose buried behind all of these parts.)

I went back and changed the tensioner again and DISCOVERED the bolt provided was a bit loose without the tensioner. SOLUTION - I put some RTB on the bolt and tightened to specs and corrected the whole problem. Hope this helps many of you save all the above work.