Definitely depends on the breed of duck. If you get Khaki Campbell for instance, the females seem to never shut up and quack frequently. Most ducks will and can be heard for some distance and are louder than most chickens IMO.
On-the-other-hand, Muscovy ducks (some are downright ugly, again in my opinion, and some are very good looking, are about the quietest breed of poultry you can have. I have 30 some, all white, and I can sit in a chair among them and close my eyes and never know there was a duck around for miles! Quiet, friendly, fair egg layers, good mothers, and excellent table birds too.
Google French White Muscovy Ducks and you will find a short youtube clip showing these ducks and let me know what you think......
BTW, I only have the White "French Production" Muscovy Ducks and am extremely happy with these. I now raise no other poultry.