i don't have the answers but i share similar experience .... and curiosity since i've tried a bunch of fixes unsuccessfully.
drbill, you say you don't have the problem but then you say:
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I have never had any problem - EXCEPT....
When I run all the electrical crap like Headlights, Heater Fan, Radio, Rear Window Defogger, etc all at once.
or
If I leave the lights on for even a few minutes after killing the engine.
Also - if your battery is old and won't hold a full charge.
My Metro leaks oil all over the engine and Alternator Belt and still doesn't squeal except as mentioned above.
If it starts squealing after I start the engine, I turn everything off and the squealing stops.
I let the engine run fast for a while to get the Belt to stop squealing and it usually stops squealing permanently.
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.... so evidently yours does sometimes squeal. mine is intermittent too but it sounds like mowfixer and others have a steady problem. all the variables mentioned could contribute i think and he says he's going through water pumps and belts unlike most of the rest of us.
i also noticed that squealing was more consistent in wet weather here in so cal.