According to the BBC, I'm not supposed to be able to hear this. But I can, very clearly. Take a listen. I presume it is the insistent oscillating high pitch whistling sound, not the background rumbling and other low frequency sounds that I'm not supposed to hear. But I can, quite clearly. Can you?
Or am I just making this all up, and there is no sound at all? It's a bit tricky, when you think of it. Equally, if I can hear it, and people say they can't, how can I be sure they aren't lying too?