I'll give it some time; I've only had it 2 days so far, so it's too early to draw many conclusions. So far I've run it in a bucket with some vinegar water for 24 hours and now have just put it in my sump.
It's definitely quieter (and smaller) than my last skimmer. I measured the sound with my iPhone and got about 50 db for the Icecap skimmer vs just under 60 for my old reef octopus. I can't guarantee how accurate the app measures levels and your ear hears different frequencies and different noises differently, so the comparison can only go so far, but the dB meter would indicate that the Icecap skimmer was about half as loud, which I would subjectively agree with. There's the hiss/rush from the silencer and a low hum from the pump. It's about as loud as my Waveline DC10000II pump, but I've heard people describe that as inaudible which it most definitely is not.