I pretty much have the same vortex fan as you (same stats, just a different manufacturer) and it's directly under the kitchen. Granted, mine is mounted to the top of my vent. hood, not to the joists, but the hood is mounted to the wall, which ties into the joist above.
Here is a pic of my vent setup before running the ducting, but you should get the idea. Not pretty and shiny like yours, but it does the job. In the kitchen, there is a subtle hum, but not bad at all. Granted it is directly below the kitchen cabinetry in the kitchen, so that may be dampening the sound as well, but my wife does not find the noise offensive thus far. I'm not sure if I mentioned or not here, but I am working on my drop ceiling tomorrow and over the weekend in the brewery. I plan on insulating the joist space above the fan and framing a box around the sides of the fan itself, so that I can wrap insulation around that as well. I'm still going to get noise from the fan from inside of the hood, but even without insulation, it's not that bad. I figure that with a little insulation and the drop ceiling in place, the noise should be minimal. It was much louder on the work bench when I plugged it in than it is up high over the hood.
Here are few somewhat recent pics of the brewery from a few weeks ago if your interested in taking a peek.
Roadie......to answer your question, I do not have my fan hooked up to a speed control switch. It's all or nothing! I get minimal steam from my HLT and MT, so I really don't use the hood until I get to the boil anyways. I have a new flat screen down there as of last weekend, and a stereo system soon to come, so that will take my mind off of the fan noise.
