Tlot-tlot; tlot-tlot! Had they heard it? The horse-hoofs ringing clear; Tlot-tlot, tlot-tlot, in the distance? Were they deaf that they did not hear?
Right after hearing about love's refrain, we hear (at the same time as Bess) an actual refrain, the steady repeating sound of horses' hooves. That's bad news, because it means the highwayman is coming back.
It's not clear right away if the soldiers have heard the tlot-tlot sound of the hooves. The tension is high.
Down the ribbon of moonlight, over the brow of the hill, The highwayman came riding, Riding, riding! The red-coats looked to their priming! She stood up, straight and still!
Now the highwayman comes riding along the road ("the ribbon of moonlight") and appears over the top of the hill.
There's a little refrain, an echo of lines 4-5 with that "riding, riding" stuff.
Now the soldiers have heard for sure, and they start getting their guns ready ("looking to their priming").