Was underhood the other day and noticed a very faint squeal. Couldn't hear it with the hood down. Took off the belt and spun everything by hand. The alternator was the squeaker, but spun freely. Replaced the alternator, belt, and tensioner and the mileage was better than ever. Previously (before it tanked) I was getting 14-16 around town. As of last tank, I was over 18. Going to run another tank to be sure it wasn't a fluke.