The Boeing 737 - 800 has cracking issues all over the aircraft including the Aft Pressure Bulkhead - Main Frames in main cabin where the overhead bins attach to the frame. Numerous cracks on the -800 main cabin Frames at the overhead bin lower mounts were discovered during the first Major Check.
[After 5 years in service]
The NG and later aircraft structures - in my opinion - do not even compare to the early generation 707-727-737-747. Lots of the major structure parts on NG's were made with lighter gage materials including frames- stingers- skins- bulkheads in an effort to save weight.
The skin and stringers above the main cabin floor line required bonded doublers called "acoustic dampeners" to reduce the vibration and buzzing of the airframe on the -800.
The ones on the stringer hats look like railroad tracks. The ones on the skin has a corrugated look.
I expect for many more cracking issues to arise as the NG Fleets age.