Now and then the flies roared softly at the screen door.
– John Steinbeck
The Grapes of Wrath, Chapter 2. The flies "roaring softly" at the screen door represents the Joad family and their quest for a better future. Although simple and humble sharecroppers, they are about to embark on a great journey across the U.S. in the hope of finding a better life in California. That epic odyssey is foreshadowed here.