Odd whine noise after ignition off 3.8L

I have a 3.8L auto 98 with 114k miles. When I turn the ignition off after it's been running a bit there'll be a pause (4-5 sec) . . . then whine. It's not a knock or grind, it's more like a squeek. Often it will pause whine pause then whine a 2nd time.

Any ideas would be appreciated.

Vacuum, clogged Cat, coolant?

It's so difficult to put an ear and pin point it.