Etymology

Alteration from べちゃくちゃ ‎(bechakucha), an onomatopoeia for a large number of people talking noisily.^[1][2] The shift from initial /b/ to /p/ changes the meaning from an emphasis on noisy to an emphasis on lively. Compare English gabble, chatter, yackety-yak.

Also analyzable as a compound of root elements:

• ぺちゃ ‎(pecha): onomatopoeia for lively talking, evocative of the sound of lips and tongues smacking; also onomatopoeia for the sound of water splashing against something.
• くちゃ ‎(kucha): onomatopoeia for the sound of paper crumpling; by extension, indicates that something is being done in a confused or disorganized fashion.

Pronunciation

• (Tokyo) ぺ​ちゃくちゃ [péꜜchàkùchà] (Atamadaka - [1])^[2]
• IPA^(key): [pe̞t͡ɕa̠kɯᵝt͡ɕa̠]