My 13-week-old Polish cockerel, Leopold, started crowing with a ghastly "BRAAAAAACK!" sound about a week ago (DH actually ran out of the house the first time he heard it, thinking that one of the birds was being attacked by something). He has now progressed to a reasonably good "doodle-doo." He'll crow five or six times in a row a couple of times a day, and quietly goes about his business the rest of the time. He's not particularly loud, actually - the girls are much noisier when they're squabbling over something.
My three similarly-aged Speckled Sussex boys (one is 13 weeks, the other two 12 weeks) have remained crow-free thus far. They are occasionally hitting on the pullets, much to the pullets' annoyance, so their hormones are shifting into gear, but at the moment all of them appear to prefer to be known as strong, silent types.