Originally Posted by
DOASO
high pitched whine coming from back which they hadn't heard before. They both said you can't hear it until the helicopter has passed by them, so they are facing the back of the aircraft.
What phase of flight were you in: taking off, cruise, letdown, etc? Were you in the same flight phase both times? Was the noise steady, pulsing, or other? Have you physically changed
anything, no matter how minor. on the aircraft since either mechanic has been near your aircraft?
Have chased many "unique" sounds over the years. FYI: Sometimes how a person hears the noise and how sound travels doesn't always indicate where on the aircraft it may come from.