Back in 2006, our ancient (19-ish years old) Whirlpool refrigerator started making weird howling noises suggested someone broke into the house and stuffed a dog inside the freezer. Turned out to be the fan behind the rear panel of the freezer compartment that moves air across the cooling coils and down into the refrigerator compartment; evidently the sintered bronze bearings wore just enough to let the shaft oscillate side-to-side while rotating.
I ordered a replacement, but then decided to try an old fix: put a dollop of STP in the bearings. That added enough damping to kill the resonance and let the old fan turn freely. It worked so well that I put the new fan on the shelf in case it came in handy later on.
Years passed… and then, as if by magic, the freezer dog reappeared.
Mary moved the contents to the downstairs chest freezer (she’s much more organized than I and wanted to find things again), I pulled the old fan out, installed the “new” fan, buttoned up the freezer, and it ran fine.
Until about two in the morning, when the freezer dog began howling again…
As nearly as I can tell, the new fan’s bearings arrived just slightly oversize; I doubt they’re pre-worn.
So I applied the STP fix to the new fan:
- Remove the compression fitting from the fan blade hub
- Remove the fan blades from the shaft
- Remove the screws & nuts holding the frame together
- Remove motor shaft from bearings
- Put a drop of STP into the rear bearing
- Slather a ring of STP around the front bearing
- Deliberately misalign the self-aligning bearings to redistribute the slack
- Reassemble in reverse order
It’s been running silently for a day, which suggests it’ll be good for quite a while…
The Smell of Molten Projects in the Morning 
May the fleas of a 1000 Camels chase away the howling dog and leave you in peace.
OTOH,
I do remember that I gently punched the bearing forcing enough metal inwards to take up the slack.
Your hand is better than mine!
I tried that on a different motor (a while ago), managed to freeze the shaft in place, and couldn’t ream the bearing out to a snug-fit diameter. For this motor, the STP trick seems less risky…
Our 2 year old Whirlpool refrigerator has been making an intermittent strange noise that sounds similar to what you describe pretty much since day 1. I never bothered to call for service because it is infrequent enough that I’m sure it wouldn’t make the noise when the tech showed up.
I kind of figured it must be the fan, but never bothered to tear things apart to confirm it. Easier to wait for a hard failure.
It could be ice on the impeller that causes an imbalance or wakes up the Freezer Owl.
If you could see the fan through the rear wall, it’d be easy to diagnose. Having to remove everything from the freezer, take out the shelves and their brackets, pull all the screws, pull the back wall, and then figure out what’s going wrong tend to slow down debugging. A lot.