2003 Dodge Ram What could be wrong?

I looked but I'm not exactly sure what it is I'm looking for. I felt a soft spot near the catalytic converter, and I saw that a plug end from the catalytic converter was touching the heat shield leaving a black mark I guess from it melting.

Ok I just checked the exhaust I only heard the vibration of the exhaust but it does not sound like the rattling noise I've been hearing. Nor did I hear any tin noises. I did put the exhaust on my self and the ubolts didn't close the pipes enough to keep the exhaust air from coming out. I tried to seal the pipes where they connect but I see black chalky stuff on the outside. Could that have had something to do with the noise? I don't want to say that the exhaust is not the problem so I'll wait to hear what you think. Back to the heatshield should I take them off to see if there's something wrong?

I reread what First posted And I don't think I said what I needed to say. It is not a constant sound just a sudden sound of like a second or two. If I hold the gas at the right place I hear it longer but not as violent, but it doesn't always sound when I try to make the noise. I let my father drive it while I listened and it appeared to come from the middle to the back of the truck so It could be the heat shield and I missed it or something else. I did look at the heat shield but couldn't simulate the noise. A question I was hoping you could answer is if air is escaping the exhaust in the wrong places could that be what is causing the sound? Thanks BMRFIXIT for your help.