I'm now on the third motor in the space of ten months.
The first motor was noisy from day one, but suffered the bearing issue, and was replaced under warranty.
The second motor was lovely and quiet until I took it swimming, then the noise of it increased over a period of a few months, until it suddenly just gave up. Again it was very kindly replaced under warranty. I hadn't expected this, so am grateful to BH for that.
The third motor, isn't even really audible at all. It is just so quiet. That is also kind of why I hate my mid drive so much. I hate the noise of it.
The Dapu motors do seem pretty mixed in respect of noise though. some are just as mine, almost silent, and others quite clearly make a noise that has owners wondering what is going on.