Spodman, I have not heard the Temora Meteor but I think that noise you refer to is the original, the one and only,
never to be forgotten, Blue Note.
It certainly wasn't produced by the Derwents because not all marks of Meteor produced this note.
The most likely reason I seen put forward for it is the aerodynamic noise around the gun ports above a certain speed combined with a sort of organ pipe noise from the gun barrels.
A number of aircraft types since have blue notes attributed to them but IMHO there is nothing like the real thing.
