I've narrowed the source of excess noise in my machine to the PSU fans. There's 2x 80mm ATE-branded (anyone heard of them?) fans, both of which put out a considerable CFM value, but also a great deal of noise. Infact, I reckon the dB level fell a couple of notches when I tested the system with a single-fan PSU!

So, I'm going to replace the fans, and I have a choice between Akasa glowy-uppy ones and YS-Tech plain black ones.

Which ones should I pick?