It's 24/7. It's more reactive than anything. It's most noticeable with background noises. There's a lot of whistling morse code. But then I also have the typical "eeeee" sound. It varies but, I'd say it might be hovering between level 3-5/10 so moderately noticable. Sometimes it can suddenly jump to a 7-8 but that usually lasts 30 seconds or something like that.