The heat shields are external...you'll know it when you see it. I would get the car up on ramps/stands the night b4 then start it up crawl underneath with a block if wood to press up against the shield or whatever to see where the rattle is coming from. These things get burn hot quickly pay attention. If it is the shield you can try pulling on it to readjust, loosening/retighten bolts or what I've done on cars where the mounts are messed up some real large hose clamps around the shells to hold them together.
2012 V6 traded in for a 2017 VW GTI.