Drakes do not have the physical ability to quack loudly. Their mature quack will be quiet and raspy, much the way that a woman's voice box is simply not capable of producing a bass sound. Female ducks have a wider range of possible sounds and you may have to listen a while to hear the quacking but in general they will be more vocal overall than males. I often find that males will suddenly be quiet and not say a thing while I'm holding them, where girls will usually start quacking right away. Typical, eh? lol But unless you actually hear the quack or the rasp, you won't know for sure. Some ducks will start quacking at 3 weeks, but it's more common at 4. If you REALLY know what you're listening for, you may be able to tell as early as 2 weeks but again, 4 weeks is more reliable. Boys will still be peeping at 4 weeks.