Maxwelg2,
WRT your comment
Without the missing section of the second stage planet gear it will never be known if this part of the MRGB was the generator of this harmonic
EC will have to capability to produce an acoustic analysis from the known design parameters. It will have been analysed over and over for all known harmonics, especially those which would interfere with all major rotating frequencies (of which there are many in a helicopter).
Whether or not a section of the gearbox is missing or not, a modal/rotor dynamic analysis will produce all possible amplitudes.
Pas.