I was looking underneath the truck to chase down the air type noise I’ve been experiencing underneath and the only thing I found of interest was this hole. It is on the passenger side, and right behind the muffler. It has remnants of a hose adapter inside. but no hose in sight.

 

My truck doesn't even have that.

 

Hose adapter? Or grommet.

Your pictures are too close and at odd angles to really see where it is. Get a wide view. The slotted hole right above it makes you think that a bolt felt out.

What's the other side of the truck look like, same position? Might be a clue.