I run both types of filters on my tanks. I have a 404 and a XP-2 on my 80, a XP-2 on my 46 and a XP-3 on my 50. I can not hear either filter unless there is a little air trapped in it after service. I must admit though that I do have a slight loss of hearing so whether or not I would hear it if I had better hearing I do not know. 2 of the 3 tanks are set up in the spare bedroom and we have quite a few visitors that stay the night and none have ever complained about the noise.
On the other hand I do find the Renas easier to service though. They are both straight forward to service, but I find the removal and repacement of the tops much easier on the Renas.The Renas also have recesses built in to the tops to carry them when cleaning.The Fluvals do not.
80 gallon FW
:3 clown loaches, 2 angels, bloodfin tetras and 1 albino BN pleco,1 Farlowella.
46 gallon FW
: kuhli loaches, otos, black neon and black phantom tetras, 3 pitbull plecos.
50 gallon SW
: 1 green spotted puffer