[BrianG]

Yeah, I did mean that the motor actually makes the beeps, but of course the ESC sends it the signal to do so. If you have the motor not mechanically hooked up, you can see the shaft turn slightly when it beeps.

I read a little bit about why motors will do this and it said (can't remember where exactly) that the wires vibrate because of the frequency. If they are tighter winds, the noise sounds muted - like in a Neu motor where the coils are wrapped around some kind of core to concentrate the magnetic flux.