Interesting.
I have used two Revo 1836 lathes and didn't notice any noise as you describe.
I went online and listened to 8000Hz tone as you suggested. That kind of noise didn't emanate from either of the two 1836 lathes that I used, otherwise I would have been concerned about purchasing my Revo 2436.
I just went to my shed and turned my lathe on to have a listen. It is a Revo 2436 and it does have a larger motor at 2.2kW (2200W) than the Revo 1836 motor.
I had my lathe running at the lower speed belt setting, and turned it on at roughly halfway, the wind noise coming from the fan at the end of the motor started to sound like the 8000Hz noise I just listened to via my computer from the web.
Turning the speed dial to 100% the lathe was spinning the spindle around 13500 rpm or thereabouts, but the motor of course was running at the limit. I moved around listening, and I have my hearing aids in so I can hear all sorts of sounds. The high pitched whine I did hear, was immediately deadened a real lot once I placed my hand over the fan guard at the end of the motor. Placing my hand on and off the fan guard, the high pitched whine sound went on and off.
While you may be hearing a high pitched frequency sound, I wouldn't be too sure it was emanating from the power supply. At least that is the conclusion I have at the moment.
If you are hearing the sound at low revolutions of the motor, then you may be correct, but in my case, and yes, on a different machine to your machine, it only occurs when I'm running the motor near terminal rpm.
