Is my exhausted/muffler bad?

I replaced the end part of my muffler a few months ago due to a crack. Recently it started to make a loud noise like it did when it had the crack. Its only been a few months, how could it have broke that fast!
Plus, on and off for over a year now my cause has been over heating problems. Its summer in miami and it is extremely hot. My car has been over heating so much! Especially if i'm on the expressway going fast. Its so annoying! I've checked the radiator a billion times and it doesn't have a leak.
Could i have a bad exhausted thats making my car over heat?
I have a '98 honda civic
Saving up for a new car now.

Did the weld break off your muffler?

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