I have an issue with a sound recording I made with my Olympus LS-12.
The recorder is recording a constant unknown sound at about 10kHz. The sound is visible in the sonagram below as a faint dark band.
Can anyone suggest what this noise is and how I can get rid of it? I've tried adjusting the gain of the recorder and recording away from my phone and computer, but this hasn't solved the problem.
I covered the microphones of the recorder with hands, to try to determine if the unknown sound is internal. This was the result: