This sound comes from Team Fortress 2 and is tied to the Heavy's Sandvich, one of the game's most memorable character items. The Heavy became a fan favorite partly because of his oversized personality, voice lines, and food-based comedy. Clips of him eating the Sandvich spread through TF2 videos, memes, and remix edits, where the chewing sound is used as a quick punchline for greed, healing, or total satisfaction. It still gets reused because even a very short clip is enough for players to recognize the joke.