[What's_nitro?]

I believe (don't quote me) that Castle uses variable drive frequency on their controllers. That would help to explain the change in the audible tone generated throughout the throttle range. They DO use variable timing in their controllers, so it would kinda make sense if the drive frequency were variable as well. Both parameters being based on the load at any given time and allowing the motor to run at maximum efficiency at any load. You know, if I'm wrong about this, it may be worth looking in to. If they (CC) aren't already.