Patent ID: 8292593

Claim:
An air-cooled server system with one or more heat-generating electrical components, comprising: a chassis housing the electrical components; first and second cooling fans disposed within the chassis and providing air cooling to the electrical components; a fan controller providing a first control signal to the first cooling fan and a second control signal to the second cooling fan; and one or more noise generators independently and randomly modulating the first and second control signals, wherein the first and second control signals comprise first and second pulse width modulated (“PWM”) signals that control respective first and second blade-passing frequencies of the first and second cooling fans, wherein the first and second PWM signals have respective first and second duty cycles, wherein the one or more noise generators cause the first and second duty cycles of the first and second PWM signals to vary in a manner that independently and randomly modulates the first and second blade-passing frequencies within a range around a blade-passing frequency set point, and wherein the one or more noise generators comprise a first additive noise source indirectly coupled to the first cooling fan and a second additive noise source indirectly coupled to the second cooling fan.