It's the noise you hear at about the one minute mark when the digger is reversing: https://youtu.be/BljL3XO0fyg?t=59

Oh this is horrible.

We don’t want people run over by reversing vehicles, but also, if I had to listen to that every day, I’d leap in front of them.

	▲	slobotron 2 hours ago \| parent [-]
		IMO, in person it's much nicer on the ears than the old single-tone beep that they used to have. It's less jarring and easier to locate where the noise is coming from, ye olde beep seemed to come from everywhere at once.