"叽里咕噜" is formed as an onomatopoeic compound where the characters mimic sounds: "叽" imitates a chirping or squeaking noise, "里" functions as a nonsemantic phonetic filler to maintain rhythm, "咕" replicates a gurgling or muttering sound, and "噜" extends the murmuring or rumbling effect, collectively creating a reduplicative phrase that phonetically represents continuous, indistinct noises like chatter or grumbling.