Post date: Nov 17, 2014 5:54:17 PM
This phenomenon is well descried in the book on page 135 -136, but it is confusing at this stage as there is three audible frequencies that can be tracked with FFT software, ears and tone generator. Going away a couple of days but I will continue study the phenomenon when I get back.
It might be bad wood, but on the other hand the frequencies are clean and sharp.