I set up a 1tb arrary for a client, with an old dual celeron 300 motherbaord and a couple of cheap pci sata controllers, all up around AU$2000, about US$1200, it runs raid 5, and has a dvd burner for their important stuff to be burnt too. SOrry but until you can show me a NAS that has 1tb in raid5 for this much, then the server solution will always be better, more upgradeable, and really doesn't draw to much more power, my file server costs me $15/month to run 24/7, so if the price difference is $100(from what I have seen it is more like 5 times this) between nas and software solution, it'd be 10-50 months before they hit the same price, in that time I could have upgraded my storage, and added security to the shares... Hard drives from most resellers here in Australia are mostly below AU$1/GB that means a tb will cost less than AU$1000 or about US$600 . So from that 1tb lacie 1ru rack mounted nas it was US$1100 for that you could almost get a 2tb file server, with raid, and probably even with a tape drive to backup important files.
I would also suggest depending on the amount of users of your file server to suit the operating system to this, windows basically makes you pay per user that connects to the file server sequentially, of course windows is easier for most people to administer, but linux/bsd can have an unlimited number of users connected to them, so it is really cheaper for mass file storage.
As for less noise, you can setup the pc to be quiet, but if you sacrafice a little noise for less overall cost and more configurability, then so be it. Also it is cooler to say I have a 2tb file server than it is to say I have a 1tb NAS, then you have to explain what NAS is and they just look at you and go why didn't you just get a thumbdrive...