Jenn Air Noisy---suspect air flow motor/fan

This is a built in unit. I have had an ongoing problem with this frig being very noisy. There is an almost continuous running sound that can be heard easily across the room. So far, three repair techs have looked at it and could not identify the problem, although they did not try very hard.

After listening carefully and doing some online detective work, I think the source of the noise is the air flow motor/fan at the top of the freezer compartment.

My question: There are four components to the air flow motor/fan: fan motor, fan blade, fan motor retainer, and fan blade grommet. In your expert opinion, which one of these components would be causing a loud motor sound almost continuously? Is it a loose retainer? Damaged blade grommet? The motor itself?

Thanks.