[The noise actually sounds a lot like... idle chatter?

Somebody down there is nattering on and on about fish! fish! many fish north! and neighbor! noisy neighbor from under! many neighbors! in a very strange tone. They do not know anyone who talks like this. Also, in between all of this chatter is another weird noise, like a low grumble or even a zipper being pulled. At this point, they can probably recognize it as a puffin's call.

If they approach the cliff, by the way, there are shrubs on the ledges to hide in, not too bad for a small duck. There's also the end of the pier. But they'll need to look down still to find their eavesdroppees(??).]