There you go Wheelie, thank you. That puts some
real numbers on my rather fast guesses, but my altitudes are about right!
Which also highlights that some of the configuration changes to your aeroplane would be happening roughly overhead SW16.
As a field engineer, sounds are part of my stock in trade and for me there is rarely 'just a noise' - I can't help analysing them to figure out what makes them. I'm a Land Rover driver, so I'm very used to trying to work out what's going to break next!
Roger.