What is Kenny voice issue?

Kenny McCormick from the animated television series South Park is known for his muffled and distorted speech. This speech impediment is a result of a parka hood that he wears over his head, which muffles his voice.

Kenny's voice is characterized by a high-pitched, nasally tone, and his speech is often unintelligible due to the added layer of fabric over his mouth. The muffled voice adds a comedic element to his character and has become a defining characteristic of Kenny.