Tunze 1073.050 noise

[Gargamel35]

What kind of noise should 1073.050 produce? Should there be just humming noise, some scratching noises or something else? Reason i'm asking this is this:

I bought my first 1073.050 months ago and it produced a lot of noise. So i got it replaced with another one. The second one produced less noise, but still developed annoying scratching noise in every impeller turn. So i hear humming noise and another noise like something is scratching somewhere all the time. Not as loud as pump nr. 1 but still there. Pump now works for more then 2 months and it's clean inside.

So i got 2 pumps so far, both are not able to produce humming noise only. Now i need a backup pump for my system and i'm not sure if i want another 1073.050.

Is any other Tunze pump quieter then this one?

 

[rvitko]

If the pump is isolated so the connections are by flexible hose and it is on the suction cup feet with no hard surface contact their should be almost no noise, maybe some hum. My thoughts would be air is trapped in the pump by an angle or restriction or that a bushing is not fully seated, the bushings should be seated in the pump and not come out with the impeller or easily but only by pulling with a tool. The smaller a pump is the quieter it will be due to less rotating mass and noise from water movement, but without going smaller for example to 1073.020, I don't think much noise reduction is possible but this pump should be fairly quiet.