The popping/clicking noises that you can hear when the HVAC system starts up or shuts down is one or more of the numerous blend door actuators. It is a common problem on vehicles that share this platform. If you are determined to fix this issue, search for terms such as blend door actuator, blend motor, mode selection motor repair. My 2010 Ford Flex (built on the same platform and shares many of the same parts) does this. I’ve chosen to live with it. Good luck to you!