So first day with the window down in awhile. I can hear a rhythmic tapping which sometimes becomes an intermittent rattle. This only happens when I am stopped and in D. Goes away in park and even in reverse. Also goes away as soon as I touch the gas and is silent and smooth accelerating and shifting.

Any ideas? Cat heat shield? Something else loose? I really don't feel like dealing with something internal but that would be my luck.

 

I'm inclined to go with a heat shield.