+1 on the rattles
About 15 years or so ago I came across a d-28 an early 60 model, at one of the guitar stores I visit when I go down to the big city.
While trying it out I happened to hear a bit of a rattle in the guitar and I was surprised to find a rattlesnake rattle, its still there btw,
Upon asking the owner of the store he told me what he knew about the guitar, I won't bother with the story .
Then I started asking around and I was told different stories, some said it was for good luck and other such things, but what I heard the most
was that it started when someone found a spider or something inside their Mando, so to scare off unwanted little critters hence the rattle, and over time it spread
to larger instruments, also the good luck story pooped up several more times.