Sparkie,
I went out and took a look at the space between the brackets on the topside of the muffler. With the car cold, the gap looks pretty close. Could close up when hot and make contact. I took some 3/4" heater hose and cut some spacers. Split the hose and wedged them on both sides around the edges. I also added a piece of rubber on top of the existing rubber mount in the center. Hopefully, this might be my rattle point. I'll let yall know. I would rather have bent the mount outward some but there is not a way to get a bar in the right place with the muffler mounted. If this temporarily fixes it, I will drop the muffler and bend the bracket.

Keeping my fingers crossed...