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Originally Posted by jlrii
The noise is sort of a buzz. It is caused by the square wave used to drive the pump.
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Yeah, it's a square-wave sounding whine. Significantly drops off in volume below about 10v, and significantly noisier at 13v+.
I suspect that it's caused by some sort of interaction between the bearing and the impellor as the magnetic fields flip very suddenly causing whatever vibrations that would cause and creating the sound.
The bearing (the D4 has just one and only one bearing) on the D4 is of a high quality ceramic, and not something that is likely to wear out very quickly, even moreso due to the nature of the design of the D4. It truly is an elegant design. Noise aside, I would have to say it is the single most impressively designed centrifugal pump out there.
I mean, at 16v it's drawing on the order of 30W or so, and performing as well as my 50Hz Iwaki MD30-RZ. The D4 is clearly built to a budget price-point though in terms of the motor body. I would gladly pay 1.5x as much for one that used the same design, ran like a D4 @ 18V (~35W - basically performing like a 50Hz Iwaki MD-40RZ which draws 110W), and used sufficient body mass to quell the noise. That would be
my dream pump.