[HoosierDaddy]

Some rectangular are straight through as well. If it is quiet enough except for the rattle which I'm assuming is the inside of the muffler rusting and coming loose I would replace with a similar design. Try using your temperature scanner to record exhaust manifold and muffler temps before and after the muffler change. I dont think egt's will be an issue but generally quieter = more back pressure= higher egt's.