On my set up, which is a copy of Rolf's, the loudest thing in not the dust extractor, it is the noise of the sucking air at the saw. Not sure what the remedy is for the. There is an adjustment on my hose where you open a hole, to reduce the vacuum. I tried opening that thinking it may reduce the noise a little but the sound made at that opening was louder, it whistled! I will live with the sucking noise, it is a minor thing to put up with to not have dust everywhere.
On the box fans, has anyone tried one of these: http://seyco.com/air-cleaners/
I thought they were expensive, but considering the cost of the little furnace filters, this my be cost effective. I thinking of getting one and using my box fan again in the shop just to catch some of the other dust I stir up working around in there.