Speaking of 3TB drives: I purchased the Western Digital "Green" drives for this setup. My initial observations of them are that (1) they are as mechanically quiet as the 2TB drives, BUT (2) they do vibrate more than the 2TB ones, and this may make them audible in some cases. I also wonder about endurance with all of that vibration.

The vibration from the extra platter is not bad -- less than a typical 7200rpm drive -- but it is noticeable when compared with the 2TB versions.