Munch

google

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late Middle English: imitative; compare with crunch.

wiktionary

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From Middle English monchen, a variant of mocchen, mucchen("to munch (food); chew audibly"; > Modern English dialectal mouch), probably imitative in origin (compare crunch). Compare also Old French mangier, mengier(“to bite; eat”), of similar sound and meaning.

etymonline

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munch (v.)

"chew deliberately or continuously," early 15c. variant of mocchen (late 14c.), imitative (with -n- perhaps by influence of crunch), or perhaps from or influenced by Old French mangier "to eat, bite," from Latin manducare "to chew." Related: Munched; munching.