Some background noise kind of like engine noise, which rising from near-DC and silence to a steady running rate, and then falls again to near-DC and silence with reverberation. This is from an Analog Box circuit created for the purpose. This is intended to give you total onset and turn-off as if switching a mechanism on and off. Unlike the others, this one is not a loop, but the steady portion can be replaced with the EngineNoiseSteady sound from this pack (which is a loop), such that if you blend the transitions and repeat the EngineNoiseSteady loop, you can get any desired length. Others built from the same circuit include EngineRoomThetaRelaxer and EngineRoomWaver, but there are also other sounds intended to fill a similar role but with a rather different character in that same Backgrounds pack.
EngineRoomOnOff.wav
聲道：2
類型：wav
falling、vessel、ambient、background、rising、engage、abox、disengage、noise、engine、synthetic
落下、船隻、周圍、背景、升起、從事、一個盒子、解開、噪聲、發動機、合成的
資料來源：freesound ( https://freesound.org )