These are 12V Sunon fans. And yes, they sound very much like a wind tunnel.
It will be going in a 1U case, but looks like I'll have to build one since Apple's price is ludicrous.

Ah, those are great fans. Hmmm, try and find any hi end brand of that size and check the specs. You may have to deal with the loudness, it is a server after all.
-maestro

OK, so these fans are are 40x40x28mm and run at 9200rpm. That strikes me as pretty fast, so I guess these are going to be tough to replace...?

Then again maybe not. I need the dB rating for these Sunons....

http://www.computergate.com/products/item.cfm?prodcd=BCFD448B

OMG! 9200 rpms, no wonder its so loud. Try going with some around 4000 and put two at each
end of the power supply. My guess, is at that speed, you wont find quieter ones.

-maestro

That had occurred to me. You reckon two running 4000 would be up to the job? I'm guessing these were used for a reason.

Isn't a Xserver a rack server?

Yes, its a 1U rack server. My guess is the fans are so fast to get enough air in that small space. Remember too that servers do serious heavy lifting. What do you plan to do with yours? By the way, xserves are far quieter than their pc counter parts.

-maestro

No matter what type of rack server it is they are loud when you have a SCSI chain and sevral running at once. I wouldn't change out the fans. Just live with the fan that's in it. Give it a while and you'll learn to zone out the fan's roar. Or you can go spend another 2 grand and get the a A/C cooler for it.

I intend to use it primarily as a media server. When its done, it will be able to stream my video collection over my home network, and hopefully over the net when needed. It will also provide numerous other services: VPN, maybe a website at some point, ftp, I'm sure there are others that will come in handy in time.

I'd also like to hook it up to an EyeTV box. (Here's an aside question: Can you hook up two EyeTVs to one Mac? Should run OK on a dual proc in theory...?)

An idea which has very recently occurred to is to build my Xserve case bigger than the standard, (still only 1U high), paint it white, hang it on a wall and hook up a projector using the case as a screen.. I would definitely need to quieten the Xserve in order to do this though.