This is a background hiss my cheap microphone records when i use my laptop. I recorded with audacity. This one has spikes of static noise every so often, sounding almost like faint voices. It's creepy in my opinion. It can also sound like water or a waterfall running in the background, or a beeping futuristic computer in a spaceship.
16 bit 44. 1khz, recorded on zoom h4n stereo. Field recording of trick or treaters in housing estate on halloween, some fireworks in background, mostly people/children talking, very background-y.
Uk birmingham canal between icc and aston, large factory with extractor fans running in 'background'. H2 zoom front mic with wind shield, hand held, some wind noise.
I recorded these ambience in my garden and didn't recognized that my laptop in my room was still turned on. So you can here voices from students returning from there break to the lesson.