I have a topfin 20 which is quiet enough for the living room but still not silent enough for my bedroom! The AC
was a dream while it was quiet; I had to touch it to make sure it was working.
I dislike my Tetra Whisper 40 as well, it's the loudest of all. My Whisper 10 is great though and has been for 4 years. Too bad the Whisper 40 couldn't be as quiet.
I'll look into Quietflow, thank you.