One embodiment of the present invention provides a system that determines fan speeds for a set of fans in a computer system. During operation, the system receives time-series data collected by a vibration transducer associated with the computer system, wherein the vibration transducer is configured to record mechanical vibrations from the set of fans. Next, the system performs a spectral analysis on the time-series data to obtain frequency peaks associated with fan speeds for individual fans in the set of fans. The system then identifies fan speeds for the individual fans in the set of fans from the frequency peaks.