Here is a quiet fan that gives other quiet case fans a run for their money.

Available in 80mm, 92mm and 120mm

 The Nexus 80 mm quiet case fan has a true 17.6 dB(a) decibel rating - measured in an anechoic chamber using ISO standards. This is one instance where the case fan's decibel ratings haven't been understated by the manufacturer.
How does the Nexus 80 mm quiet fan measure up?

This Nexus 80mm case fan is extremely quiet. According to our own listening tests, this fan is quieter than any other 80 mm quiet case fan on the market (including the Papst 8412ngl). Yet, it measures a decent 20.2 CFM airflow level and is available at a reasonable price. This quiet fan also includes the added advantage of both a 3-pin motherboard power connector and a 4-pin standard power connector. This versatile case fan is truly worth its weight in gold.

Nexus Real Silent 80 mm Case Fan Specifications
Model	SP802512L-03
Power Connectors	3-pin and 4-pin
Dimensions	80x80x25mm
Weight	85 Grams
Rated Voltage	12 Volts
Operation Voltage	10.2 ~ 13.8 Volts
Input Current	0.15 Amp Max
Input Power	1.8 Watts Max
Rotation Speed	1500 RPM
Acoustic Noise	17.6 dB(A)
Airflow	20.2 CFM
Operation Temperature	-10 to +70 C
Storage Temperature	-40 to +75 C
Manufacturer's Warranty	3 Years