Old but quiet (Score 4, Informative)

For years the huge cooling fans like those on board train locomotives have used a neat trick to keep the noise down. Instead of placing the fan blades at equal angles from each other, they are offset by a small amount. This actually results in a lot MORE noise but it's all outside the human hearing range. The same trick works for small fans as well but no one ever seems to take advantage of it. You basically hear nothing but the motor. (By the way. Does anyone know if there is a manufacturer of these in existence? My computer could definitely use a fan upgrade.)