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Old 15th Apr 2019, 13:35
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Join Date: Dec 2001
Location: FL, USA
Posts: 2,291
Keep in mind also that engine noise is now no longer reflected by the runway surface so they may appear to have been throttled back but that is not the case.
If climb obstacles or other climb profile requirements allow it a thrust reduction is done at Flaps 5 or 3000í.
As far as the rumbling noise I can only guess:
Runway surface
New tire and worn tire on the same gear truck
Flaps 20 take off and some play in flap mechanism transmitted through the wing.
Floor boards and seat tracks causing a little harmonic vibration.
Youíre sitting pretty much right above the Air Conditioning packs.

Could be any and all of the above and maybe another dozen I didnít think about.
The airplane is fully alive at that time, youíve got bleedair going allover the place, hydraulic pumps running, electric motors the whole kit and kaboodle.
No doubt under certain conditions it will generate a little harmonic vibration somewhere down there.

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