looks like the aftermarket exhaust hangers are causing the muffler to sway to one side causing the muffler to come in contact with the bumper

 

Any half-decent exhaust shop will have a wide range of rubber exhaust hangers so drop into one and check them out. It looks like all you need is a pair of slightly shorter hangers, say one or two cm shorter than the existing hangers.

 

Is there a question?

 

I am pretty sure you're using the wrong hangers, try this one.

 

This IS the problem. In your second picture you can clearly see the second peg that the the three hole hanger is supposed to hang on. The incorrect hanger is pulling it to the side. They DO fail, and are easy to replace.