Chick voice change

[1dude]

I have two chicks that are bigger than my 10 week olds, I guessing they are 12 or 13 weeks maybe. I got them from the local crazy chicken lady no idea the age. Any way a couple days ago they stopped cheaping and now sound almost like ducks. A real nassely sound more like an adult hen. Any idea what age they do this at?
thanks
duder

 

[1dude]

I did a search for this before and couldn't find anything. Today I see lots of posts about it.
Anyway 2 of my 4 EE's voices are changing. They are 13 weeks, so if this is common then my other ones are probably almost 4 weeks older.

 

[Den in Penn]

Never been able to pin down an age where their voices change. I think its like starting to lay, they will do it when their bodies are ready and ever one matures at a different rate.