People usually go to school or work or destination on usual street. View and sound that they can get are always same and boring when they walk on it. If the sound change new sound, they can explore usual street and get different feeling.
Onomatope is a way to express specific sounds by words in a comic. It gives people strong impression and makes them imagine the story easilly. Onomatopes are based on original sound. But you feel different from original if you hear it. And you can enjoy weird and rhythmical and poppy by onomatopes.