One idea that has occurred to me recently, is to use a USB 3.0 hub and a bunch of nearly-silent external USB 3.0 "drives" -- the WD "My Book Essential" units in particular.

Our local electronics recycling depot came by a pallet load of empty "My Book Essential" enclosures, and is reselling them at $7/each. Since I have a shelf full of bare SATA drives here, I've purchased ten of those enclosures.

With a WD "Green" Drive installed in one, the thing is darned near silent. Cooling is passive -- no fans, no noise. Even purchased "new" with a 2TB or 3TB drive included, these are only about a $10 mark-up over the bare drives.

The bare enclosures do seem to work with any size/brand SATA drive, not only the WD "Green" series drives.

Cheers