Quiet fan with change them well suited for Zyxel NSA325

I have these fans ordered as a replacement fan for Zyxel NSA325, without knowing in advance whether it works well. I Mini Kaze fan installed and NSA325 turned on, the fan noise is barely noticeable, unfortunately hear periodic, quiet high-frequency sounds that are disturbing to my mind as an original fan noise. The NAS shows fan speed to 0, and sent warning fan too slow when you set delivery alerts. The CPU temperature is slightly higher than the original fan, at maximum load ca 54C, which means passing to a lower air throughput to CPU. I have reinstalled the original fan.

Nevertheless I forgive 5 stars because of the fan itself is quiet and caused the high-frequency noise by controlling the fan speed by PWM.

Update: December 4, 2013

When there is the fan directly to 12V connects no more and air flow rate is higher than with the original fans buzzing as CPU temperature between 37 and 45C is. Noise is lower than with controlled original fan. In German Zyxel Forum describes how to rewire NAS must link is in the comments.

Update: March 12, 2015

After about 2000 hours operation at 12V fan is louder, especially when turning. By not optimally geförmten fan blades pull this magical dust. Due to increased noise I change my rating to 4 stars.