Rattle on Startup Fix

I've been noticing that when i start my truck it rattles for a few seconds then stops rattling, regardless of the temperature it is started at. At first i thought it might be a cat going bad, but i decided to check my heat shields before i jumped to any conclusions, so I crawled under my truck and wiggled/ tugged on all of the heat shields and all of them felt good and tight. So then i decided to take the back of my maglight and lightly tap them and see if I could notice any of them having a different sound to them. I tapped them lightly and sure enough the heat shield on the drivers side by the second cat had a vibration / rattle sound when tapped. So i then proceeded to remove the three 10mm bolts that hold it on and carefully removed it. I found that underneath were small pebbles/dirt and debris that were causing the rattle.

I cleaned the debris off the shield and reinstalled it. While reinstalling the shield I noticed a loose bolt that holds the support/brace around the exhaust. I'm not completely sure what its function is but maybe someone will chime in with more on that. While i was under the truck I also tightened it, it is a 12mm bolt. i started my truck and the rattle was no longer present. Thanks for reading! Pic of the loose bolt below. Also a couple more in gallery.