[MagicRat]

Good points.

I have noticed my older cars creak, groan and pop much more in the cold. Some of this is the effect on adhesives, some I think is because the ride is stiffer, due to more rigid tires and shocks.

As for structural fatigue, this reminds me that most older Fox-body Mustangs I have encountered develop floor pan cracking behind the driver's seat. My old '79 V8 Mustang had massive cracking that I had to weld up. I noticed the metal was 'work-hardened', like dented and hammered body work, as Curtis says.
Even my '87 4 cyl Mustang had this same problem.

Other cracking examples.... second-gen Camaros and Firebirds would sometimes develop cracked roofs, especially the T-tops