What is this weird sound from the GMAC hub motor? (video)

[youtube]PQGjnrCfc_E[/youtube]
I have a couple of other videos on my channel showing the same sound, if you didn't think this video was good enough.

What do you think this sound could be?

I can't find anything in the gears that could make this sound. And there is no sound when I turn it slowly by hand (the noise starts at roughly above 100 rpm) Also, there is always a gap between the gear sides and everything else at all speeds.

The motor seems to work almost perfectly when I use it in the bike. Only thing wrong is this annoying sound that comes when coasting and that when I apply max regen, there seems to be something weird happening when I come down to about 10kmh (like a momentary loss of braking force)

I tried taking out the hall sensors and running without them. Same sound. Both when running sensorless and sensored (I have a phaserunner) I also applied full throttle to bring the motor to speed, then I unplugged the motor while it was spinning quickly and the sound continues while the motor spins without electricity.

The phasewires are also fine. I tried putting them together in all combinations and that made the motor clearly harder to turn around by hand.

Which makes me think it is mechanical!

When riding the bike, I could only hear the sound when the bike was coasting. When I used throttle or regen I didn't hear anything wrong.



How it started:

The sound started happening after I let my brother use the bike. He went full speed up 800m of 8% gradient with 52V and 35 Amps. Then he drove fast down again and used maximum regen available. That is when the sound happened. He also drove quickly over a speed bump, perhaps while applying max regen.

I tried to run the bike myself and applying max throttle, then max regen, but the motor cut out in the regen phase. I then had to cycle the battery on and off to get it going again.

It was probably very hot in the motor. But the temperature sensor doesn't work, so I don't know how hot.
There is some hard plastic-like stuff on the left side of the windings that looks like it shouldn't be there and has melted.
How do I remove the bell-like piece that holds the permanent magnets?

Photo of the melted plastic-like or glue-like stuff on the windings: https://imgur.com/BU9McnX

I got to add that I can actually hear some sound when I listen closely and just move the motor around by hand. It sounds like it comes from the blue gears, which is confusing because the look totally fine.

Maybe the gears themselves are not lined up, maybe one is off at an angle.
Also check the gears on the small middle gear and its alignment.
Clutch could be toast.

To eliminate any potential for the noise to be coming from a defective gear, maybe run the motor with 2 of them removed. Just run 1 at a time - at no load of course.

Or remove all 3 of them to see if you still get the noise?

Dynamo Hum.

Last time I heard that sound was from a Magic Pie that was overheated with one phase of lower inductance and resistance. The time before was in a Frank Zappa song.

Spray a little lithium grease or WD40 on the gears and clutch while its moving and stay out of the spray - if the sound doesn't change its not likely mechanical.