What is causing the clicking noise and is it expensive to fix?

This may be the cooling of metals after the car is turned off and it is no longer producing heat. Heat expands metal, and it contracts as it cools. Engineers know this when they design and chose the metals to use in an engine. It could be the exhaust system also since a lot of aluminum is used, also the catalytic converter cooling will do this as will the brackets holding various parts. Open the hood of the car and bend over the fender or front and listen to isolate where the sound comes from.

Could be blend door module inside middle of dash

I had this same problem on my fiances impala. My coworker stuck his head under the dash for a few minutes and fixed it right up. I have no clue what he did. But i know what you're talking about and thats where he was when he fixed it. I think it took him 5 minutes

Pleased help me with my Ampala the noise IS killing my battery Helps

How do I fix this problem