Concerning "elderly" HP48G/GXs :)

[freelanzr]

My 48G (Singapore, blue screen) does make the same 'creaking' noises you report, and it has certainly become worse over time.

I would assume that heavy use and occasional drops have contributed to some small amount of plastic deformation at the stakes and latches, so that the calculator is no longer as tightly held together at the seams as it was when new.