One of the best quiet and at same time, kind of high CFM fans are the Noctua. They are also available in non-PWM fitting the SE3016. I have seen numerous Norco's cooled down by them and they are pretty though to cool.
Anyone tried to open up the PSU in the SE3016 and use the main 80 (or swapped 120mm) fans to cool it in addition with the disks?
I have not tried this, and would not recommend it unless you have this in a climate controlled room. The PSU puts out a fair bit of heat, and even without the top of the enclosure on, the rear case fans will have a hell of a time cooling both that AND the HDD's themselves.
The only way I can see that working, is if you installed very high CFM/RPM fans, and then it would defeat the purpose, as it would still be loud.
Installing the 40mm Noctua fan in the PSU really is the best option. It's not that much work, only takes a couple minutes to disassemble the PSU. You just need to splice some cables (with a soldering iron preferably, but you can just use twisted wires and electrical tape instead if you're really lazy).