just thought I'd pop in here if you're still looking, I've had a lot of luck with IBM eServer pSeries SCA SCSI drives for low noise. I've just recently ordered a 10k 73GB + SCA to 50pin adapter to go in a PowerTower Pro 250 Mac clone I recently acquired, and I already own two 146GB's of the same kind in an old dual PIII server in my posession. they are among the quietest SCSI drives of their time (2005ish? depends on how lucky you are) and they last pretty much forever given they're kept relatively cool.

I"ll keep you posted if it turns out to be quiet enough.