That is a normal happy chicken sound. My chickens make numerous sounds, and yes I can tell the difference in all of them. Chickens are pretty smart really. They have learned that looking in the window and making noise gets them a treat. Make sure they have a variety of food available always and stop giving treats that way. There are different sounds for "just laid an egg", predators, hungry etc. if you pay attention you will learn them. I see no rooster in your flock, looks like all hans to me.