Is muttering onamatopoeia

Muttering is not typically considered onomatopoeia. Onomatopoeia refers to Words that phonetically imitate or resemble the sound they describe, such as "buzz" or "hiss." While muttering suggests a low, indistinct sound, it doesn't mimic a specific noise in the same way that onomatopoeic Words do. Instead, it describes a manner of speaking rather than a sound itself.