咿 often appears in the reduplicated form 咿咿呀呀 (yīyīyāyā), describing baby babbling or incomprehensible speech. As a standalone sound it mimics a squeak or creak.
Left mouth radical - a pictograph of an open mouth. Carries the meaning: 咿 is a voice sound, used in onomatopoeia like 咿呀 the squeak of a hinge or a baby's babble. Indexes 咿 in the noise-making family with 啊 ah, 哎 ay, 嘿 hey, 呀 ah.
Right side 伊 supplies the sound - yī stays yī with no shift. The literary pronoun meaning is not active; 伊 is purely a sound tag, chosen because the bright yī syllable mimics a high squeak. Almost the entire usage of 咿 is the doubled onomatopoeia 咿呀 and 咿咿呀呀.
