I'm posting the problem and RESOLUTION here. The correct title will make it more searchable.
The problem arose as a hi-pitched screech or chirp sound coming from the engine after warm-up, and whenever the RPM got up to 1300-2000.
It sounded so much like a failing belt idler roller-bearing, the natural impulse was to grab a stethoscope....all the pros who looked at it fell for that theory.
This "chirp" was a ruptured membrane inside the PCV oil trap (long black box covering valves, top of engine near windshield). No wonder it couldn't be located with a stethoscope! More typically, the sound is a steady whistle. In any event, to diagnose it, you merely remove the oil filler cap and the sound silences in response.
This is a simple repair anyone can do. You have to replace the PCV oil trap and gasket ($170).
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