Your probably not used to the sound of that much air moving. I've never run a Dayton 465 but I used to run dayton 265's so I'm familiar with the product and I currently run a couple 6" vortex's. There is no way that a properly functioning 6" vortex is mechanically louder than a dayton 465. They simply move more air and pull harder under load thean any squirel cage style fan. Get a speed controller...I'll bet that when the vortex is moving the same amount of air as the dayton was that it will be quieter.
nothing wrong bro. I have a 6 inch vortex as well and it is definately loud. Its a loud steady drone even when pulling through my carbon scrubber.. Just build a DIY silencer. Basically a big tupper ware style bin with some kind of batting material to insulate the noise and 2 holes.
I always thought that speed controllers sacrifice performance. Your basically downgrading your setup by slowing the air movement to quiet it down. Its nice to have a controllable fan for sure. I have a dayton controller I had purchased but have yet to try it out. I also have a "silencer" I built for next to nothing and it sits on top of the cab making the Vortex mostly quiet while pumpin all 465 cfm's
Isn't a 6" vortex running at 449cfm's? if so, I don't see how it should run any louder than a dayton 465 since it is already moving a little less air. Try a speed controller, put on a muffler, or push through the carbon scrubber which will muffle the sound greatly. I have a dayton 465 in a cabinet and push through the carbon scrubber and it greatly muffles the noise.