To conduct our noise level tests, we replaced the graphics card in our system with a AMD Radeon HD 5550 Silence which was passively cooled. We also momentarily disconnected the fans on the CPU cooler so we were only taking into account the noise generated by the fans in the case. We tested the system with the fans at the maximum and minimum setting.
We can see that even with the fans at full speed the case remains pretty quiet. The inbuilt fan controller can decrease this down to an inaudible level, though.