Squealing Noise

Buick Century, 2002 model, 151k miles, squealing noise under the hood when engine is under load. First suspect, serpentine belt. Replaced, no joy.

Next suspect, vacuum leak. Checked vacuum lines by spraying starting fluid on the lines at idle. No joy.

Up on the rack, noise appears to be coming from vicinity of the starter, but it's really hard to localize.

Anybody?????

Anything with a bearing will sometimes cause a squeal. My water pump caused a squealing as did the alternator. Also ckeck the idler pulley.