Well, just got back from inspection. The loud noise I was experiencing was a leak in my flex pipe, an almost $1100 part. Luckily my GMC dealer recommended a very good shop that does welding and who also just got a brand new bender. Yay. It'll cost me $125 including labor instead of the $1200 it would have. Also found out I have a rust hole on my left rear rocker that need a piece of sheet metal welded onto it. No biggie like the exhaust leak though. I was sweating it out for a couple hours for sure this morning. Also learned i'm idling a little high according to the tech. Hopefully it will be because of the leak, but i'm also putting a new IAC valve that I bought a few months ago on Ebay into it. Hopefully those two things will correct the problem. Damn, this tech was thorough.