Aerocool Streamliner Silver 140mm Fan 54.7cfm 19.6dBa
Evercool Red Scorpion 140mm Fan 68.2cfm 22.1dBa
Scythe Zipang 140mm Fan 52cfm 21dBa
Of course they are manufacturers specs but you could not run them at full speed to acheive less than 10dBa which is all the Noctua does to get it's quietness (ie runs at 800rpm when normally it runs at 1200rpm)
Plus I find anything less the 15dBa is inaudible, never mind 10.
General background noise in a room is 19dBa.
Hope that helps, not many around to choose from at present. The Aerocool do different ones with different coloured leds btw.