High-pitched whining

[Antshark]

When I used an old MSuper, I noticed a constant high-pitched whine. I thought nothing much of it, but then I noticed that in videos, KS and Gotway unicycles often emit a constant high-pitched whine when turned on. I know little of hardware, but is this the sound of the MOSFETs?

My regular vehicle is an InMotion V5, and I don't hear this sound. A recent post observed that InMotion and Ninebot EUCs seem to deliver power in much smaller intervals. Does this imply that I can't hear them because the MOSFETs are making a much higher frequency sound?

And finally, the real question I'm curious about - why isn't this complained about more? It annoys the heck out of me. Are people just indifferent to the sound? Do they actually not hear it (maybe Gotway enthusiasts are old enough to not hear in range *hem*)?

 

edit: Actually, varying search terms made me realize that yes, the high-pitched sound does receive some amount of attention - but I'm still curious as to whether I'm correct about why I can't hear it from my InMotion. This particular thread was interesting: 

But I don't know if it was very conclusive (and I don't wish to practice thread necromancy)

 

[dmethvin]

The whine on my KS14C is definitely near the top of my hearing range, I generally only hear it when I'm riding next to a hard surface that reflects it to me like a fence or a truck. I have noticed that on quiet streets that younger people with their backs to me sometimes look back when I am getting near which leads me to think they've heard the whine. I should ask some time!

As for where the noise comes from, I thought it was the windings of the motor vibrating from the high-frequency power switching that EUCs do.  The way the windings are driven by the circuit may also have some effect, there was some discussion of that here: