Hi Peter,

The mpeg didn't play for me but just a few thoughts:

Since they say they couldn't reproduce it on the ground, could this be a
noise issue? Possible sources would be the radio, a transponder
transmission, engine ignition, maybe a motor driven trim, fuel equalizer
pump if you have one. Just think about other stuff on your aircraft that
produces either RF or commutation noise and comes on automatically and
possibly unnoticed by the pilot.

I have seen such noise become a real problem with composite structures.

Regards, Joerg

http://www.analogconsultants.com