A320 Groaning Noise

Date:         19 Feb 97 02:46:21 
From:         cp@panix.com (Charles Platt)
Organization: PANIX Public Access Internet and UNIX, NYC
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Recently enjoyed my first flight on an A320 (via America West, out of
Newark) and noticed a prolonged groaning noise that began shortly
after takeoff while the engines were running at high power. The noise
sounded like the kind of groan you sometimes hear briefly when wheels are
retracted (if you're sitting right over the wheel wells), but it lasted 5
to 10 minutes, finally fading away when the angle of ascent leveled off.

The noise returned during descent and lasted another 5 to 10 minutes.

I have heard a kind of "buzz" from engines or resonating airframe on
a 747 when it climbs after takeoff, but I'd never heard anything like this
groaning sound before.

Is it a well-known feature of the Airbus, and if so, does anyone know
what causes it? I'm just curious.