Loud continuous Screeching from attic

Good day all. Attached is a video we took last night of a mystery sound coming from our attic. We live in Ohio for weather reference. It’s happened periodically in the hot summer, and again a few times on and off last night with 32 degrees outside. It may last a minute, maybe 5 minutes. And it can also be heard from outside the house. Electrician said the attic fan is old but doesn’t seem to be an issue. He’s coming back today to look. We’re thinking a bad bearing in the fan? This video is from a hall closet which has the attic access door in the ceiling.

Here is the video