Hello. I know that it is probably hard to see because it's a small picture. If you zoom in a little on your internet browser you should be able to seem them better. At the end of the selected interval (EH1), underneath the semi-sinusoidal wave form, on the spectrogram, you can see two rows of ripples. In fact, you can see them throughout the entire window, but they are more visible where I have indicated.
Does anyone know what these are?
This recording was done on an H4n and 44100Hz in a attenuated booth. The H4n was plugged into the AC wall charger.