You have to suspect a "sympathetic resonance" from some part of the aircraft at certain speeds/altitude and throttle settings. I once read a report that on the first flight of TSR2, Roly Beamont (the test pilot I believe) and his observer in the back, suffered vision problems as they wound up the jet for take off. Investigation, it said, found that the Hydraulic pumps were resonating at a particular throttle setting at the same frequency as the human eyeball. Now, although it seems fanciful, we've all had ornaments etc rattle from a bit of "over zealous" speaker volume. Could that relate to the "Blue note" at all ?
Smudge
