Inline duct fans aren't really designed to handle much back pressure. In other words, they suck with carbon filters. If there's much of any resistance in the ducting, you'll fry the motor over time. You need a centrifugal fan for use with your carbon filter. I have only tried one brand of those myself, EcoPlus, in both 4" and 6" versions. They aren't incredibly quiet, but I don't think any centrifugal fan is going to be all that quiet. They are relatively cheap compared to Hurricane, Vortex, et al, which is why I use them. Plus, they've been very durable; I've had a 6" EcoPlus 440 CFM fan going 24 hours a day for two years now, with a speed controller attached to dial down the speed, and no probs at all, still going strong.