Can software cause this?

[HemiRoar]

About 2 months ago, updated my Trinity and installed the 91 performance tune. Right away, anytime I hit a bump or rough pavement, I had this plastic thump from behind the radio..more towards the passenger side..that area. Sounded somewhat like squeezing an empty plastic soda bottle. It drove me crazy, had a dealer tech open it all up and he did re stow some loose wires but it was still there. Everything was tight. Recently I realized that when I have the A/C or heat on at the windshield only option, the thump goes way.

This morning, I put it back to the stock tune and the thump is gone. Cabin is all quiet again.

...Can anyone make sense of this?

 

[cgeorgemo]

You have a loose blend door.

 

[HemiRoar]

You have a loose blend door.

Thank you. Now I can tell the tech what to fix!