I like the way Jenny the T and SharonA explain the line. No other explanation made as much sense.

I misunderstood the rest of the verse at first, but I agree with you, SharonA:

Line 6: The child (who was to become the narrator) remembers the uniquely deep rumble of the souped-up engine after his Daddy and uncle finished their rebuild.

7: A sheriff came in the night, to tell Mama about Daddy's accident.

8: Mama's reaction woke the child, and forewarned him of the bad news he was about to hear.

9, 10: The last lines of the verse about Daddy give images of the scene which ended his life.

The vivid sense of Daddy's character and the narrator's home, the irony, powerful imagery, and the natural way in which the "Copperhead Road" refrain and other structural elements of the song fit into a compelling story, all show the writer's mastery.