There is a method, system, and device for diagnosing an anomaly of a monitored component in a drive train, the method including obtaining original data based on samples of a vibration signal and a tachometer signal; generating a time synchronous average vibration signal; processing the time synchronous average vibration signal to produce a frequency-domain spectrum; determining the complex magnitudes of the frequency-domain spectrum; selecting a sub-synchronous band of the complex magnitudes of the frequency-domain spectrum to generate a sub-synchronous spectrum; and determining the mean of the sub-synchronous spectrum to generate a condition indicator.