A couple of exhaust questions

I occasionally hear a rumbling/scrubbing sound coming from under my truck during very light throttle, such as easing through a parking lot, so I climbed under there to look around a bit.

My truck does have headers and a Dynamax muffler, but right below a cross brace was a piece of heat wrap fabric wrapped in aluminum tape. I have no idea why it was there since there's not even a seam there. Is there supposed to be any wrapping there?

 

Also, just forward of the muffler are these two seams with a bit of soot showing. Does this look bad enough to cause any odd sounds?