What to do

Kids/babies screaming on purpose is about the most annoying thing to me.....BOTH my kids are doing it right now while they are suppose to be taking a nap. Lukas was never a screamer. That is, until my little Lydia came along and started screaming. Now Luke joins in all the time. Why it annoys me I don't know. But it does. Bad. You would think its kind of cute that they do it back and forth like they are talking and bonding..... No. Nope. Not working. I hate it. How do I stop Lydia from screaming?????