We measured noise levels 1" from the SN25P's front, side, and rear using an Extech Model 407727 Digital Sound Level Meter. Measurements were taken after 10 minutes at idle, and then after another 10 minutes of a Folding@home CPU load. We also measured noise levels with Shuttle's XPC SB95P V2 and SB86i for comparison. Those systems were equipped with a Pentium 4 520 2.8GHz processor and Radeon X600 XT graphics card, but otherwise had similar hardware to our SN25P. The SN25P and SB95P V2 used their default Smart Fan setting, but the SB86i requires its Mid fan speed setting to maintain stability under load.
With an Athlon 64 3500+, our SN25P system is much quieter than either Pentium 4 520-equipped XPC. That isn't a particularly surprising result. However, notice that the SN25P barely gets louder under load, and that's not even with Cool'n'Quiet enabled.