Quietest 6" In-Line Fan?

The quietest fans I have found are hands down CPU or radiator fans, yeah the ones that go on the back of your cars radiator. They are run on DC not AC so you need a power inverter, but they are made to be quiet, and have massive cfm ratings.

Hyper Fan still looks like the one to beat. I still wish there were flanges on both ends, but duct tape works, too.