In the video you are pushing the starter button with the lever, which engages starter pinion with the flywheel. You were supposed to just push the button for one of the tests. So the video is not that test, correct? The video is the same as your foot pushing from inside cab, correct? You are showing what the starter does under normal conditions and you still confirm that the button only test still makes starter spin fast, correct?
I didn't hear a whine.
So something electrical is breaking down. (I guess that is mostly obvious.)
To wit:
1. A connection
2. A cable
3. The switch mounted to starter
4. The battery
5. The starter
6. A ground
7. Lug on inside of starter, that button makes contact with, is burnt down/worn down, breaks down under load.
Or hydraulic locked motor with water in the oil/cylinder
Or Screwed up valve train
It's always the battery in these situations and as Jerry says on a no start, it's always the points. You are not in a "no start" yet. You are in a "no crank"
If you say battery is brand new I hope you don't mean reconditioned or something other than a brand name new battery because it's always the battery. See if it still has 6.2V-6.3V.
The battery cable I see in the video looks strange, like too small, too flexible, too old? Not sure but don't like.
