Hi Alex. I have just update the firmware and no sound is listened yet. So, I think the problem is microphone as you pointed.

Hi Alex. AudioMoth was bought on July 10, 2019 at LABMAKER

I see. Thank you. I'm going to update a newer version. Actually, in this file that I have sent to you I talked during the record, but no voice is listened.

Hi. I have recorded this file. When I put in a program to see the spectrogram no signal of sound is seen. About your question, I'm waiting for an answer of my coworker. Thank you

Hi. I have a similar problem. The device records at the right time, it creates the file, but no sound is recorded by it.