My first batch is 6 weeks old. Their quacks are very distinct now. I have VERY loud honky quackers (girls) and males- raspy low sound makers not even a quack...a couple of the males only make a sound if you scare them or hold them.
mine have a difference in quake's but its so close to me that i cant really tell and they dont seem to quake at the same time for me to get a real good listen