I bought an Aquarium filter a while back and I had to send the head back because it was very noisy. It was returned with a new impeller but it’s still noisy so I’m now in contact with the importer. There is only one moving part on these pumps, it’s an impeller with a tubular magnet with plastic vanes. This rotates on a ceramic shaft. In operation there is a humming noise and vibration coming from the head. I have a similar unit from another vendor and it’s virtually silent. I’ve measured the ceramic shaft with a mic and it’s 2.48mm. Sorting through my drill bits I found the end of a 2.56mm bit just fits in the impeller opening. It doesn’t sound much but the gap between the impeller and shaft is quite noticeable in the hand. What would you expect a reasonable clearance to be for something like this. Anyone have any ideas? It may be that something else is causing the noise but I can’t think what that may be.

I’m not prepared to do it at the moment but next time I clean my other filter I will check the clearance on that just out of curiosity.