A thump and beep occur, then the low hum of an industrial motor ensues and is ongoing.
A machine starting and is running at a constant speed. A machine starting and then running at a constant speed. A thump and a beep occur, and then the low hum of an ongoing industrial motor ensues. A thump and beep occur, then the low hum of an industrial motor ensues and is ongoing. A vehicle is being started up and left running.