Clicking noise Key Off

[CROW]

Truck is a 2018 Tradesman all of 33k miles without push button start. Know this sounds strange but both the wife and I have heard this distinct clicking noise when the key is not in the ignition. Almost sounds like an electrical switch opening or closing. Noise lasts a short period or time _guessing couple minutes-and then stops. Could be coming from the lower front of the engine. Have not been able to crawl under the truck when it is making the noise so could possibly isolate the noise.
Truck starts and runs just fine with no check engine light.
Any ideas on what where I should start to find the problem

 

[Ozymandias]

No problem - DEF system purges the circuit back to the Tank.

 

[AH64ID]

Several things click after shutdown, the def injector (back near rear axle), EGR valve, or intake valve.

 

[Turbo Terry]

Yes have notice some of this myself