I have a 2007 cobalt ss supercharged 6400 miles on it the motor knocks when you start it up the oil is milky it have burned 2 quarts of oil and the dealership said theres nothing wrong with the car I am going to another dealership but im sure the head gasket or head is bad but i still cant figure out the knocking noise it only does it when the car first starts not every time it starts but alot of the times i love my car and just would like to know whats wrong

 

Coolant in the oil. Head gasket is blown. Have them do a differential pressure test.