"Brinson"
hdds= noise
best bet for silence is get a mini-itx case and get one with slot load drive bay (slimline 5.25") and an internal 5.25" bay. In the internal 5.25" bay add a hdd cage and place a operation harddisk e.g. a 40gb sata drive to house any temprorary files and operating system place this harddisk into the hdd cage then use a wireless or even bluetooth linkj to connect to a file storage computer which is alieanated from the main machine the storage computer can be very low spec e.g.
cpu: intel pentium (600mhz)\
ram: 512mb
hdd: all hdd space you would need say 1.5tb in raid0 or raid 5 (bear in mind raid 5 adds data protection and speed increase combining all disk space but you need a minimum of 3 disks and the largest hdd is subtracted from the combined hdd space so 3x750gb = 1.5tb of usable space whilst 6x750gb = 3.75tb of usable space
psu: 200W
OS: your preferred linux as its free.......
network card: depending how you create the file share connection could be bluetooth, wifi, lan, infrared lol whichever (infrared would not be pratical mind)
you can make network folders default so in essence you never have to save anything on the mythbox except the boot os