Panorama of multiple bat call events (50+ seconds).
Several pulse trains and buzz-stop events, all in the space of 1 minute.
First 10 seconds of picture 1.
Seconds 14-16.5 of Picture 1.
Seconds 33-37 of Picture 1.
Seconds 42-45 of Picture 1.
Seconds 45-53 of Picture 1.
The buzz is such a featureless sound that it is worth a closer look.
It is also possible that this is some kind of detector artifact.
This is the FFT spectrum on a dB scale. The highest frequency is 16 khz (half
the sampling frequency) and the spectrum shows a broad peak around 4 khz.
This also matches the (probable) maximum sensitivity of the voice recorder
in the audio range but in the ultrasound range (x16) this is beyond the piezo
detector's sensitivity peak at 40 khz.