At first I thought it sounded like the wind. There is not much else that makes noise at night around here.
Like all of the houses which are more than a couple of years old, our roof boasts a towering TV aerial, held in place by a series of guy ropes. The big aerials are no longer needed for TV reception, but most people have left them there and the local birds appreciate the perching spot.
When the wind blows from a particular quarter and with considerable force, it sets up a thrumming in the guy ropes. It sounds a bit like someone revving a truck engine, endlessly.
But on that night, I realised that there was no wind. The tonal wind chimes on the back deck hung still and silent, and there was no rustling in the gum trees.