I serviced the motor about a year ago and didn’t notice anything alarming inside. One of the bearings was a bit dirty and rusty, but I managed to clean and lubricate it, and the noise doesn’t quite sound like a bad bearing.
I can only hear it on alternating pedal pushes. If I just jump on one pedal, there's no sound, but if I shift my weight from one side to the other, it appears. I'm starting to suspect it might be coming from the motor mounts - maybe there's some flex and it's rubbing against the frame - but I'm not sure, and I don’t really know what to do about it either. Sometimes the noise disappears entirely, while other times it gets exceptionally loud.
All I know for certain is that it's not the pedals or the cranks. I cleaned the mounting surfaces and bolts with acetone, but that didn’t help. Then I tried the opposite and greased them, but that didn’t make a difference either. At this point, I really don’t know what to try next. I’d rather fix it myself than take it to a bike shop.
The bike is GZR Black Raw and the motor is Bafang M400
Yeah, this is always a good one! It's why I always recommend working cheap to expensive (usually quite an efficient way to spend working time too).
I used to alarm customers by flexing their frames to show them the creak couldn't have been their BB and was in fact a contact point (usually saddles or sweated-on stems).
Bikes are surprisingly bendy if you're not expecting them to be!
The worst "surprise creak" I ever had was in my first year as a jobbing tech - turned out to be a dry QR skewer! Thankfully I had an ex-pro race tech to help me out.