Scoundrel’s attorney receiving a rap (3-1-3)

I believe the answer is:

rat-a-tat

I'm a little stuck... Click here to teach me more about this clue!

But I can't explain it at all! Could you help me understand?

(Other definitions for rat-a-tat that I've seen before include "Knocking sound" , "Noise of knocking" , "Rapping sound" .)

I've seen this clue in The Independent.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.