I'm sure my motor has a different pole/slot combination but there is one particular speed where it gets much louder and you can feel it vibrate the whole bike. Under low throttle, it's still there but barely noticeable. Above and below that speed, it's pretty much silent.
I don't think there's much you can do to reduce magnetostriction. Oriented grains probably helps. All iron with a varying magnetic field will expand and contract a tiny amount. More current = more flux. It's like hitting a bell. Your stator can resonate. Stiffening the structure or adding some form of damping can greatly reduce it.
Does your controller have a sine wave output? I'm assuming so, since a trapezoidal controller is loud at all rpms.
I don't think there's much you can do to reduce magnetostriction. Oriented grains probably helps. All iron with a varying magnetic field will expand and contract a tiny amount. More current = more flux. It's like hitting a bell. Your stator can resonate. Stiffening the structure or adding some form of damping can greatly reduce it.
Does your controller have a sine wave output? I'm assuming so, since a trapezoidal controller is loud at all rpms.