The brain is designed to process signal and if there is none it will sometimes make up its own. I guess you can compare it to dark current in photo-multipliers.
People who have tinnitus will hear the sound you describe or something similar all the time. When I was little I had the same experience as you, but now I have developed tinnitus and never get rid of that sound any more. Sometimes it also becomes rhythmical which very annoying. The only thing that helps is to ignore it.
People who have tinnitus will hear the sound you describe or something similar all the time. When I was little I had the same experience as you, but now I have developed tinnitus and never get rid of that sound any more. Sometimes it also becomes rhythmical which very annoying. The only thing that helps is to ignore it.