Mechanical ratchet noise in both wheel wells after turning vehicle off

Hello! And I welcome all your experience! I have a noise in both of the rear wheel wells that is getting progressively louder. When I turn the car off after driving quite a bit and it's warm, there is a mechanical ratcheting noise that can be heard in both wheel wells. At first, as odd as it sounds, it sounded like a mooing or creaking. I took it to the dealer mechanic and he was stumped when he listened to the recording. It did not replicate after our test drive. Intermittent and best heard when hot. Thank you!

 

Just metal contraction when cooling. Could be the exhaust or some heat shielding.

 

On a 2016? Mine brand new made a bunch of noise while new but it settled down after couple months.

We need to hear the clip or we can't really help.