A splash, a few plaintive quacks, and then just the coursing of the sewers.
I actually rescued a bunch of ducklings from just this sort of situation once (minus the rats). Had to lift off the grate and everything. They were panicking like buggery but I got all seven of them out eventually. And before you go getting the wrong impression, my sole motivation was the fact that my very attractive flatmate was the one who came pleading to me, in quite some measure of distress, to please help the poor little things. So, sorry sewer rats. A man’s gotta do what a man’s gotta do. I’ll pay you back another time. Promise.
Textbox: Daisy loves all her ducklings, but she's in deep with the sewer rats. And they're always hungry.