Another! D5 vario pump top. Shootout Time?

[wdrzal]

correct for its a dc/ac pulse phase motor, the sound you hear is the coils energizing @ a frequency

note when change setting on the vario different tone/pitch

When changing RPM if the frequency change is from the pump and not the motor, it's usually due to hydraulic pressure changes witch apply lateral force on the impeller. One of the things a volute does is help Balance the hydraulic pressure inside the pump head. Most pumps have a "sweet spot" (RPM wise)
if it's motor noise thats different.

In my first life I worked as deep mine engineer. pumped a lot of water.

Eric would be able to determine pump noise from motor noise.

BTW nice compact design Eric, can't wait to see the finished product