Jumping In! My tank diary begins.

[Delphinus]

I run Icecaps (DC) in one canopy and Orions (AC) in another. The Orions are actually quieter. The Icecaps are neat though in that they come with heat sensors and will run at slow, medium or fast speed depending on temperature. At the slow speed I couldn't hear them, but when my halides are on they switch to 110cfm (the max speed) within seconds. They do make a bit of a noise at that speed (could be worse, but we're not talking "whisper silent" unfortunately).

I think one thing to try, when you mount the fans onto your canopy, put some small o-rings over the screws to act like a bushing or whatever the term is, they'll (hopefully) suck up some of the vibration and prevent it getting transmitted to the hood.

It's amazing how a simple oversight here or there can accumulate into a lot of tank noise. One of my canopies just howls sometimes, it's because it just barely touches one of my sump return pipes, and the vibration is transferred to the hood and it just resonates.

There's never a shortage of "Oh I never thought THAT would happen" moments in this hobby, you'll always make it better "next time" and even then you'll still think "Dang, I wish I could have forseen THAT such-and-such happening..."