2007 Pontiac G6

When I turn my car off there is a clicking noise coming from under the car that is very loud and lasts 2-3 minutes. I have been told that the clicking is the car cooling (expansion/contaction of metal). My dealership said the G6 is "notorious" for that. I agree to an extent. I know cars click when they are shut off when warm but I have never heard it last that long or sound that loud. I work with a guy that has a G6 and his never does this. I am wondering if the car is getting too hot. Recently the head gasket cracked and a month later the radiator split. My warranty just ran out. Could you let me know what this is and if it could be a problem in the future?
Thanks