I saw that on FB too. I know AR is a small company so I'm trying to cut them a little slack because I really do like the bike.
I had to send a "Any news on this?" once after sending the recording. I was expecting that they'd ask me to do more debugging but instead they told me that they were sending me a new motor which was shipped a couple days later.
Btw, the motor is a Tongsheng TSDZ2. It's possible that you might find someone on YouTube complaining about the same noise there. I looked but didn't see any fixes beyond replacing a plastic gear in the motor. I sure hope that the new motor doesn't have a plastic gear. I don't want to dismantle things again.
By the way, we had slightly worse experiences with my wife's M-class. The brake tube on that was too short and pulled every time you took a turn, causing all of the fluid to leak out. Getting them to send me all of the parts needed to fix that took a couple of tries over a couple of weeks. They sent me a brake bleed kit but it was pretty much (#*$& so I ended up buying a better one from Amazon. Feeding a new tube through the frame and bleeding the brakes was actually kind of fun.
Update: Old motor is out and new motor is installed.
I needed to buy a crank puller:
Pedal cranks came out pretty easily. I'll be billing Ariel for that part.
Here is the instructions they sent:
1. Take the battery out,
2. Unscrew the crank arms,
3. Unscrew the motor cover,
4. Unplug all the connectors in the motor,
5. Unscrew the motor and take it out.
6. You can install the new motor in following the same steps as above in reverse.
It wasn't clear to me that 3. was what was required to unbolt the motor so I spent time looking for other bolts. Just my stupidity though.
I also thought at first that the new motor had fewer wires than the old but it turned out that one of the wires I thought was coming from the motor was not. There are five wires coming from the motor and it seems like it will be easy to reconnect everything. Not so easy to get everything stuffed in neatly though. I took a picture of the wires before pulling out the motor.
There is an added step to the above: Unscrew the chain guard. There are two bolts that attach the chain guard to the motor. Those are on a track and can be adjusted. I had a hard time getting the chain guard back on after reinstalling because the track was positioned more counter-clockwise than the one on the original motor.
My wife is pretty angry that we bought an expensive bike which needs to be fixed but I'm actually kinda enjoying the learning experience.