What would cause a 738 to creak like a submarine at depth?

[mustafagander]

I wonder if the sounds could be the movement of the locating thingos for overhead bins etc. as the fuselage expands/contracts during a pressurisation cycle? The B747 classic flight deck used to be nearly symphonic sometimes as the FE's panel moved around. The Boeing fix was to grease the locating dowels. It worked!!