constant hiss in screencast

Hi I get a constant hiss with both the Linux screencast programs I've tried. I assumed this was to do with my microphone, so I've unplugged it, but I still get the hiss on playback. I also get a pop noise at the very start (and often at the very end) of my screencast videos. (Not the sound of me clicking the mouse!)

I've tried Kazam and RecordMyDesktop. An example is attached -the microphone is not plugged in.

I hope I'm not missing something obvious. Thanks for any thoughts.

Attached Files

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  Clik here to view. test.mp4 (176.3 KB)