Here's the old pics I have of how I bent the mounts for the exhaust. Im 99% sure thats your noise. Mine did it all the time. Thers one next to the rear of the trans that can be bent with a pry bar but theres another one thats a pain I used a rack and a "hootie" pole. You could also use a floor jack as well.
This is the mount by the trans. You can see at the bottom right of the picture how close the exhaust and cross member are.
Bent this mount up as well to give the exhaut more room. Its near the rear of the cab.
