When I was really little, our family got a gentle rains fountain. It had a horseshoe-like hole in the back, and a somewhat round hole in front. It came with the pump the one we’re supposed to plug into the wall. However, we didn’t know what to do with the pump. Only plugged it in, it made a really awful noise, but after we figured out that we needed to put it inside the water, the noise thought of Wound down. It was a really loud, high pitch noise, around 520 Hz, or something like that. Surprisingly, it didn’t sound like that again, even when we took it out of the water. Instead, it just made a 60 Hz hum.

  • Maybe it was meant to use water as a lubricant, coolant, and sealant. This is more of a mechanical question though. – DKNguyen Sep 1 '19 at 2:23
  • Do the instructions say "do not run dry"? I bet they did. – Harper - Reinstate Monica Sep 1 '19 at 4:18
  • I don’t remember, and anyway, I wouldn’t be able to read it, I am completely blind. I didn’t have access to a computer at that time, so I did not have a way to download the manual electronically or scan it. – HeavenlyHarmony Sep 2 '19 at 3:26
  • I use a fountain pump to remove rainwater from my pool cover in the winter months. It's very loud when not totally submerged, which is an effective way to tell me to turn it off after it's removed the water! – Steven Crain Sep 9 '19 at 3:06

It might have been a diaphragm pump. These have a small magnet attached to a flexible membrane and driven magnetically by mains current through a coil.

They’re meant to vibrate at the mains frequency, with the moving diaphragm pushing water.

The inertia of the water prevents the magnet from moving too far. Without it, the magnet moves until it hits a mechanical stop with a bang, then goes back the other way to make another banging noise. At 50 or 60 Hz rep rate, it ends up making a really loud buzzing noise.

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The magnet rotates with the incoming mains frequency .When there is no water there is no lubrication of the plastic coated magnet and the plastic housing .Water is a good lubricant for plastic parts .Also the water muffles some of the remaining sound .

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