div-1 (3s, 23 kb mp3)
Two batty pulse trains recorded with a simple/belfry division detector.
The trains repeat approx.every 1.7s
The pulses within a train repeat at an approx. rate of 12 per sec.
The audio frequency within each pulse is 3.3 khz corresponding (x16) to an ultrasound frequency of 52.8 khz (see last picture).

Closeup of the first 3 pulses of the first train.

Closeup of a fragment of the first pulse.
The sound frequency within a pulse is close to 33 cycles per 0.01 s, or 3.300 hz; this corresponds (x16) to an ultrasound frequency of 52.8 khz. The sonogram, of course, agrees with this.