"One of my biggest concerns is noise, and most of the multiple (3-5) drive enclosures available have some kind of noisy fan." I use a DROBO 5D [ . . . ] and it is very quiet, just a low low frequency hum when it is really busy. I have it on my desk next to my computer.
I use a Drobo 5N—as an archival and back-up device, not as a primary filestore—which I assume is the same enclosure as the 5D, and I'm also quite favorably impressed by how quiet it is. Unfortunately, for those in an Apple OS X (or other UNIX environment), Drobo's implementation of the SMB file-sharing protocol is, to put it as charitably as possible, nonstandard. Although it runs on embedded Linux and uses the open-source Samba software suite to implement SMB, the Drobo's configuration automatically and quite nonsensically modifies the permission bits on files transferred from computers that employ a UNIX-style filesystem. So while the content of a file will be intact after a round-trip between a Mac and the Drobo, the file permissions won't be the same as they were before the file was stored on the Drobo. I have several other Samba-based file servers (and have used many more over the years), and this is the first one I have encountered that exhibits this pathology.
There are workarounds, including the NFS filing add-on I'm using, but they're not supported by Drobo. I've been in contact with Drobo customer support about this issue and, while the company acknowledges this nonstandard behavior, the support reps I spoke to were not able to provide a schedule for fixing the problem—or even a commitment to do so.