Engine turned off.... Clicking

[nyc1dxo]

2009 with 48,000 miles

After a short ten minute ride, I shut the engine off and start to walk away from the car when I hear a loud clicking coming from under the hood. it lasted for 5 to 10 seconds then stops. Its been happening a few days now. What's going on?

 

[ceric]

Likely CAT (cat converter) cooling down quickly due to low ambient temp.

 

[nyc1dxo]

It's definitely a mechanical type of switch, or solenoid turning on and off in quick succession.