This is the result of some white noise recorded from my iPhone, stretched drastically from the PaulStretch Effect in Audacity. That's pretty much it for this sound, nothing else.
*If you download this sound, please write in the comments what you used it in!* 空洞 聲道:2 類型:mp3 Creepy、soundscape、horror 爬行、音景、恐怖 資料來源:freesound ( https://freesound.org )