My maker-x 6354s do the same thing at higher power/speed but it’s from both motors. It ends up louder or quieter depending on where the motor mounts are at so I’m pretty sure it is just constructive interference making it sound louder.
When I temporarily had two different motor mounts on the board the sound wasn’t an issue/ wasn’t noticeable but with the motors side by side it is loud enough to notice. I don’t think it is loud enough to bother other people and it is so much quieter than my old hub motors ever were so it doesn’t bother me