I think that Concept 2 have not specified noise levels in dB because rowing intensity vary. When rowing the chain and sliding seat feels smooth and makes very little to no noise. It is mainly the damper fan inside the housing you can hear. You hear a rhythmic sough from the spinning fan.
The flywheel noise level is relatively low depending on training intensity. The spinning fan is not cooling you while rowing. The air is only felt if you stand in front of the rower.