I've seen that corn head grease recommended, my only concern is that it is for low speed applications below 1000 RPM. I think the M560 exceeds that with its two-stage reduction.
I agree that the source of the noise is the stator/rotor assembly. Not sure about the cause though, maybe it has something to do with manufacturing tolerances, but in my opinion it's more likely the PWM frequency of the FOC controller.
I've not seen any hard evidence of a silent M560, just reports.
This may be explained by the subjective nature of noise perception and the fact that some riders are using low pedal cadence around 50 RPM where the noise is tolerable. Also, in city environments the motor sound is drowned out by the background noise.
If your test is successful I will open mine up again

There is a one way bearing there, maybe that's why it is smooth in one direction.
Wow, interesting. So they are changing grease for different batches at the factory?