Okay good people, I’ve finished my work and came to a final amateur conclusion.
I removed the clutch and greased the one way bearing. Everything was in excellent condition. Blew out small amount of dust, ?dogs? In the clutch were clean and had no looseness or slop. The new Gates belt was in great shape. Checked fluids in both diffs and the trans; all good
Road it around without the cover. Took some video. Tried both 4x4 and 2x4. Tried it with both belts.
Results: the Gates belt was clearly quieter. The high pitched whining was exactly the same. It was not any louder with or without the cover!
The noise was the same in four and two wheel drive.
Same on asphalt and dirt.
My conclusion: probably not the clutch. Probably not the front diff because it would be different in 4 vs 2 wheel drive
Probably transmission noise since that wouldn’t change between 4 or 2 wheel drive.
Like some of you have said, Can Ams can have lots of strange sounds. Their mechanical build is very beefy.
Working on the mechanics is impressive; working on the plastics is depressive!
Thanks so much for all your help and support!