You won't be able get an idea of gender till about 4-6 weeks old. That's when their voices change. A female will quack and honk. A male will make a raspy noise.
At about three weeks, someone started honking. Then over the next month or so, everybody started honking, then quacking, except it wasn't really quacking. My Runners make this ah AH AH Ah sound most of the time, and quacks are for when they are startled.