A method monitors operation of a disk drive. The method includes providing
a disk drive which includes a rotating disk and a head having a read
transducer in proximity to a surface of the disk and an adjustment
mechanism which controllably adjusts an average relative spacing between
the read transducer and the surface. The method further includes
generating a read-back signal by reading from the surface using the read
transducer. The read-back signal includes a high frequency carrier signal
having an envelope that is modulated by a lower frequency signal. The
method further includes varying the average relative spacing between the
read transducer and the surface using the adjustment mechanism. The
method further includes analyzing the envelope in the frequency domain
and detecting an emergence of at least one frequency component of the
envelope within an air bearing resonance range of frequencies.