I must admit I'm feeling a bit smug. I really thought someone would straight away come on and say; 'Stupid boy Rog', its the Internal Change Over Low Pressure Flange operating - duh!'
But they haven't.
I like the '757 slats opening' momentary resonance - that could be it and there are enough 757's, Lord knows. Is that about right for distance from touch down?
Mark 1's 'Compressor blade interaction tones' are interesting, because it seems to me the noise is preceded by a short, quite quick 'down doppler' engine effect, very suggestive of slowing rapidly. I always think of it as 'dropping out of warp', but there is an element of 'hoot' about it.
Keep the ideas coming guys, lets see if we can get a definitive answer, because I
really want to know.
Roger.