How did the word pipsqueak originate?

Answer 1

source: http://www.word-detective.com/back-n.html

"Opinions on the origin of "pipsqueak" vary quite a bit. The late John Ciardi, a gifted poet and etymologist who sometimes went a bit too far out on a limb, traced the term to a small German artillery shell of World War I. This "pipsqeak" projectile supposedly made a "squeaking" sound before the "pip" of its explosion. However, a definitive refutation of this theory comes from the Oxford English Dictionary, which documents the earliest use of "pipsqueak" as being in 1910, several years before World War I. I'm actually glad that this theory was disproved by that citation, because it seems very unlikely that anyone who had heard an artillery shell explode would describe the sound as a "pip."

Most likely, "pipsqueak" is what linguists call an "echoic" word -- a word that imitates the sound of something, like "bang" or "whoosh." "Squeak" itself is an "echoic" word, as anyone with squeaky shoes can attest. "Pip" has long been used to mean very small things, from the seeds of an apple to the little marks on playing cards. In fact, "pip" was originally a variant of "peep," the sound a baby bird makes. "Pipsqueak" thus perfectly describes the "squeak" a "pip" might make under stress"

When a bird begins to hatch from an egg, the hole or crack that appears in the shell is called a "pip." The process of emerging from the egg is called "pipping." While still in the egg, the little chick makes squeaking noises. Therefore, a "pipsqueak." Now the word is associated with anyone small and/or insignificant.

Answer 2

The entomology is from about 1910 meaning the trivial noise a young or weak creature makes.