What could cause a low humming vibration from the floor on a long flight?

[Oliver35]

I was on a pretty long haul flight the other day and noticed something I can't quite figure out. During the cruise, there was a distinct, low humming vibration that seemed to come from the floor for about twenty minutes, then it just faded away completely. It didn't feel like normal turbulence or the engines spooling. Has anyone else ever experienced this kind of intermittent resonance while at altitude, and have a clue what system might cause it?

[HannahMW]

That sounds like resonance from a panel or duct rather than a fault in the engines the noise can start and fade as a structure settles into a harmonic.

[VictoriaFB]

I have felt a similar thing on a long haul flight the hum is soft and then it vanishes it left me thinking it was a cabin resonance from airflow rather than something broken.

[JerryGR]

From an engineering view a quiet intermittent hum could be a natural frequency in a floor panel or duct being excited by air flow or wing movement during cruise resonance is a common explanation.

[LoganLC]

Could it have been a distant background noise from the air conditioning pack or a shelf or panel vibrating a bit the timing makes me think of resonance rather than a more serious failure.

[Ella43]

I am skeptical that this is a floor fault and not a path issue the sound can travel through the fuselage from a distant source and feel like it came from the floor.

[LaylaZR]

It might be useful to frame this as an acoustic resonance byproduct of the cabin thermal cycle rather than a problem to fix right away you may not hear it again.

[Madison.W]

Has anyone else noticed a similar pattern with a certain altitude or aircraft model perhaps it is a normal quiet phase of cruise rather than a mystery.