*Goku arrives on namek* "Ah...now it's so peaceful!" *Krillin in distance* "HELP! WE'RE GONNA DIE! HEEELLLP!" Goku: "That sounds like a duck! That's silly!" Krillin: "Quack....quack..." Goku: *gasp* "That sounds like Krillin! Hold on!!"
So to answer your question, ducks don't quack, Krillin does.