History & Etymology
Obviously this word is imitative. It sounds like what it’s supposed to describe, but that doesn’t mean the word originated in modern english. This onomatopoeia reaches back to the Germanic language that English comes from. Of course it start as a reference to flatulence. Even the earliest attestation listed in the OED is from Chaucer Nun's Priest's Tale in 1390 it was used to describe the sound a horn makes.
Of bras they broghten bemes, and of box, Of horn, of boon, in whiche they blewe and powped.
One connection I always wondered about when I was kid was the term poop deck on a ship. There really was no connection. The imitative word for flatulence came from germanic but poop deck came from French and Latin for the stern or rear of a ship.