The sound absolutely creased us up
I know what you mean WestEndGirl.
Where I live they come out at about midnight. Unfortunately this coincides with my last ciggy and a brandy out on our terrace while Mrs Makum gets ready for bed. When we first moved out it was weeks before I managed to drag a rather annoyed Mrs Makum from the bathroom in time to hear them. For at least 4 weeks she thought I was loosing the plot! In fact after about three weeks of it I began to think I was loosing the plot!
As you say (and the audio link proves) such a strange noise and more worryingly it so difficult to describe to someone without giving them the impression you are stark raving mad
So not only is this thread informative it's also providing a much needed service to the poor soles that may think (like I did), that this noise comes from the bottom of a brandy glass!
Rest Assured its real folks. Look up and you will see them in the night sky.