Scroggins, as a licenced engineer and inspector of structures for more decades than I care to mention, I would say this:
There are many creaks and groans in aircraft, especially in plastic trim, as has been mentioned. Much of this is normal and no cause for concern.
But there are also chances that frame to skin and frame to stringer cleats, ties and brackets crack and let go, causing more flex than should be in adjacent structure.
As you are an experienced pasenger, and found these noises to be abnormal. it was correct of you to notify the airline concerned. Reviewing, and possibly following up with a physical inspection, on any number of pax concerns is better than one structural failure in flight.
Happy flying.