One thing to note on the reviews. Most of them are probably written about the Prizm Classic. The current version of the Prizm that is out is the Prizm Pro or Prizm Pro Deluxe. If your reading a review its good to first reference how old the review is and what model of Prizm they where using.
I have a Prizm Classic. now when I got it there was no such thing as a "Classic" model since they only had 1 model but when they did a redesign the old style became the "Classic" style.
Mine does make some noise but I would not classify it as nosiy. I ran the skimmer in my bedroom when my 20 gal
tank was in the beedroom. When I moved to a new house we put the 20 in the dining room area (not because it was loud but because our new bedroom was less roomy with our new furnature).