turbofan noise

From:         jbn@apple.com (James B Nichols)
Organization: Apple Computer Inc
Date:         22 Nov 94 00:42:59 
Followups:    1
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I was wondering, what is the source of that pronounced, droning/growling
sound one hears when a widebody is climbing?  It seems to start about 30
seconds after liftoff and lasts for about 10 minutes.  It is particularly
noticable on the DC-10s...