The first two fans on this list are 2.5 years old, and got a lot of use the 12-15 months. The new-style SilenX fan with the tough plastic just came this afternoon. The GW is not only new but a newly released product. The Arctic Cooling 92x25mm fan is 2000RPM nominal; I just bought it. Data is fan ID, fan voltage, fan noise level at 1/4" from center of intake hub, the sensor RPM, fan size, and the range used for measurement on the manually ranged SLM.
SilenXbrit"11" 12.0V 48.2dBA 601RPM 92mm 30dBA range
SilenXbrit"14" 9.69V 49.4dBA 601RPM 92mm 30dBA range
SilenXtuff"11" 6.76V 41.0dBA 601RPM 92mm 30dBA range
GW NCB 8.63V 48.4dBA 601RPM 92mm 30dBA range
A-C AF9225 6.60V 47.6dBA 601RPM 92mm 30dBA range
Under my self-imposed rules (to not be affected by traffic noise) I could have (and probably should have) awarded a 40.1dBA to the "tuff" fan, becuz it hit that reading 3 times. But the fan spent more time at 41.0dBA, so that's what I wrote down. Noise floor right at 30dBA (20dBA range).
Do you see how quiet this 92mm fan is at equal airflow to the other "brittle plastic" fans? I suppose it's possible the plastic isn't
what makes the difference, but in 3 examples, that plastic is associated with very low noise, lower than the noise from comparable products.
I think it's worth looking into for anybody who's really serious about fan noise. You can't tell me the regular fan plastic is noisier just by leaving out the color "filler", and then tell me the vastly different plastic SilenX is using in most of its product line now makes no difference at all.
If you want the cheapest "tough plastic" fan to experiment with, Newegg sells a 60mm SilenX for $9. The fan has open ears, so you can use dikes (diagonal cutters) to nibble-away at the front 4 ears without destroying the usefulness of the fan. Warning: the 120x25mm SilenX fans may or may not be using "tough plastic" these days.