I've deployed my device as part of Silent Cities project and while in testing the config I realized that electronic noise is being recorded. I'm using the requested project configuration: sampling rate = 48kHz, low Gain. I've attached a sample wav file.
I'm using regular alkaline batteries and the pack voltage seems ok to me.
All the best,
Paulo
Just to add that the same noise pattern happens with SanDisk A2 Extreme V30 U3 (the red/gold microSD) for the same config.