thank you, that was very helpful. you are 100% right.
the problem i face most of times is pump buzz/hum/rattle, which for some reason is ignored in reviews and seems to not show up in dba levels. The 100i pro for instance, inaudible for me at 1000 RPM. However it buzzes at 1500 RPM, while reviews state that it should be inaudible at idle.
Ill try to look for more youtube videos where i can actually listen to the pump working.