Hood making Sounds when at stop sign?

[Jason Y]

I just replaced my radiator today. After driving home there was steam in the hood. It was clear so I guess it was just evaporation from the heat/cold cycle of the new radiator? Also when I stop at a redlight, I can hear sounds coming from the hood. Like a banging sound. I dont know much about cars so even if I open the hood I wont be able to tell what is what. I am going back to the shop to get it fix in a few days, but just wondering what it is to be safe.