My stock Kuro fan became noisy after about a year of use. Tried the oil trick, worked for a while and then the fan failed completely. So I looked around for a replacement.
It seems quiet fans with the third control wire are a bit hard to find? So I went with a Zalman fan mate for my voltage drop and a Scythe Mini-Kaze for the replacement fan.
The mini kaze id pretty loud (despite claims) without the fan mate, but with a bit of fan mate adjustment it’s near inaudible.
You can mount the fan mate inside with a bit of double sided tape like so:
I have a 320 barracuda in my Kuro, it’s pretty quiet, no crunching. And they are tough as nails. However I can tell you that the new Samsung spin points are the quietest, I put two in my home server the other week. I can hardly hear them. Have a read on http://www.silentpcreview.com/
BTW as per the wiki if your running he stock fan try slowing it down with:
/bin/echo -n '\\\\' > /dev/ttyS1
Put it in a startup script, and have it slow on boot.
Hope this helps.