In an expensive gaming laptop I expect them to keep it cool obviously but ow loud do they get when you start to do some CPU and GPU intensive stuff like BF4 on Ultra?
It really does depend on the system. Some, like the ASUS g750, have such good cooling there's no need to run the fans at a high speed. Other systems have to run their fans at high speeds to keep the heat out. Things to look for are thick bodies for good heat dissipation and large air grilles for the same reason.