How do you have it undervolted? I undervolted all my case fans to 5V with the molex connectors, but that seems like it would be counter productive noisewise based on reviews I have seen.
I used to undervolt with an fan controller, a Scythe KM03-BK Kaze Master Pro 5.25 inch Fan Controller
, i also have undervolted with Zalman FanMate2
, and lately with Asus motherboards and FanXpert2, here is a run on an Asus Maximus VI Gene on a CHA_FAN header (fake 4pin, aka voltage controlled) of the Scythe GT AP15, you can see in the bottom square that it idles at 323rpms even though its a 1800rpm fan, it undervolts very well,
SPCR did find a zone on the AP14 that had some noise, i cant say that i have notice on my GT15, but if you can get the 1150rpm, i think thats a good range, above 1000rpms are very noticeble imo, below 700rpms they start to get very good, but will depend on your cooling and your intentions.