Speaking personally, noises that I can locate the source/direction of are easily ignored. Noises that sound the same in multiple locations/appear to be coming from everywhere are _much_ more annoying (I once had a fridge that produced a whine that was right of the cusp of my hearing -- both in volume and frequency -- and I must have spent a good 20 minutes tracking it down because it was impossible to ignore - it sounded the same from anywhere in the room until I got within a few inches of the source). If it's a noise similar to that, I can see it potentially effecting people's sleep and having knock-on health effect.

If it was louder, some may actually find it easier to ignore. I can sleep easily with either a quiet room or with a loud room fan on, but if there's just the fan noise from my NAS I find it much more difficult.