The Poseidon 4 is very quiet.
I'm running it on a 110gal. with 2X250 wt. DE halides inside a hood. Also running are a skimmer pump, an Iwaki 40, and a Tunze Stream. The 4" variable speed fans are running on the slow speed and the tank is 80deg. w/the lights on. Many variables here but I hope this helps.