If it's just the squeal, then do like Dana67Dart said; plus I'll add this: even if the belt is correct, and it's adjusted properly, sometimes you just need a new belt. Cheaper ones can be harder rubber, older ones lose their grip (don't we all?), and if it was out of adjustment for a while it could be glazed now... especially since it's a single belt. And even a little glazing will cause a squeal now and again. (This also applies to serpentine setups.)
