I use μMoth to record bats.
With the sampling frequency at 384 kHz I always register regular disturbing signals. If I lower the sampling rate to 250 kHz it doesn't happen to me.
It looks like a disturbance produced by the micromoth
I attach sample files.
Thanks for suggestions
Paolo Debernardi
SanDisk Ultra might also be a bit slow for 250 and 384kHz recording. Most LiPo batteries will give good performance. Be a bit wary of powering the uMoth (or AudioMoth) through the USB socket. It will work okay but the 5V supplied by the USB can be quite noisy. It depends a lot on the power pack or computer.