My group bought two AudioMoths in the last round (1.1.0), having used them previously with the Nathusius Project. I flashed ours with the Nathusius Project firmware.
When I test the Audiomoths at home they work fine, and give good, clear recordings. However, I have now deployed them twice, in two separate tunnels, for a total time of 4 weeks (although perhaps using the same AudioMoth both times), and all the captured recordings have been seriously broken-up with electronic noise.
The initial recordings that capture the excessive noise of deployment are broken up (as is usual), but otherwise seem normal, and at this point there is no electronic buzz. However, every single captured recording afterwards (basically starting as soon as I leave the tunnel) has a loud electronic buzz. This buzz is from 0 to 30KHz, and always kicks in suddenly at the 0.1 second mark. Before 0.1s each recordings seems fine. What I presume are bats at 85KHz play back as crude electronic bleeps.
Yet, when I tested an apparently faulty AudioMoth at home on the same day as I retrieved it, and using exactly the same batteries without even having removed them, the AudioMoth gave perfect recordings.
I have used fresh batteries, and different makes. I am using SanDisk Extreme 64GB SD cards. The AudioMoths are in a hard plastic box as is used by The Nathusius Project, and with an added silica gel packet. Both tunnels have been damp, and my only thought is that the AudioMoth/s malfunction in damp places.
The electronic noise can be seen below 30KHz, but only after 0.1s.
99% of the recordings are nothing but this electronic noise.