strange sound from 2002 GC ES

Spent a week in the hot >110 degree Las Vegas desert area. At least we had underground covered parking.
The morning we were ready to leave I turn the key to accessory ON and I
hear a high-pitched whine/squeal from under the car. Made a sharp whine that faded when the key was turned on.
I started the car and the whine/squeal was constant. I checked under the hood, revved the engine a bit, walked around the van and listened underneath. It seemed to come from the right underbody, oppostie the fuel filler (left side). The exhaust on the 3.8L 2002 runs down the right hand side, but I didn't see anything that would be emitting the sound.
Turned off the engine - silence. Turned key to ON, momentary whine/squeal. Turn key off/on/off/on/off/on .... repeated squeals - and a "no error" flash on the dash. Restart car and the whine is constant [again].
After a few miles it stopped and has not re-emerged thankfully. Any ideas? Never had heard it before, and with 110k miles on it I want to be proactive if possible.
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