Tapping noise in rear 2008 LS

I looked in past topics don't see one like this. Forgive me if there is one.

Right after I start the car (2008 LS), I hear a mystery tap noise for about a minute or two. It sounds like someone standing at the rear of teh car and taking two fingers and tap... taptap... tap... on the side of the car. It is not affected by driving or idling the car.


My initial thought was the engine pulling on the parking brakes while at idle. But I heard while driving as well.


The only other thought I have is something with the rear suspension or a (crossesfingers and makes a hex) a mild misfire/backfire.

Thoughts?

When you do start the car up, leave it in park and go to the back to see if you can hear anything from outside the car, something might be knocking around somewhere.