I don't know if you plan on having a 'utility shelf' at the top of your cabinet or not. (Pretty handy to have, I stash twist-tie line, wire cutter, remote thermometer, digital ballast, small oscillating fan, power strips, timer, etc up there.) If so, that gave me some problems with my fan (a 6" EcoPlus fan). The fan had mounting brackets attached which were simply too large to fit in that space. It also says you can hang it with big rubber bands, but the space I had to work with was a bit too tight for that too.

What I did was take off the mounting brackets, and cut a hole in the utility shelf. I then put down weather stripping around the hole, and laid the fan onto the weather stripping, with the fan's intake duct flange hanging down a bit through the hole. You can sorta see from this pic. The whole lay-fan-on-weather-stripping plan worked really well in terms of damping vibrational noise. The fan isn't actually screwed down or anything; just its weight and tightness in the hole I cut, and the ducting attached to the top (exhaust) and bottom (intake) holds it in place.