New muffler...

Recently my exhaust has been rattling at idle. At least I think it's the exhaust. It's coming from the rear of my jeep. Also, it makes a loud droning noise at certain rpms (around 1700). I think my muffler is rusting out-not for sure. Could it also be my cat? I have a stock muffler from a '99 Dodge dakota R/T and it is about the same length as the one on the jeep. Would it be okay for me to use that muffler? The inlet and outlet on the r/t muffler are roughly the same too. Thanks.

I would crawl under the Jeep and inspect the exhaust system. A rusted out muffler should be easy to spot.

There's no indication on the outside of the muffler, but I was thinking that the baffles on the inside could have come loose or something. I've tried pulling on the exhaust pipes underneath the jeep and I couldn't get them to rattle on anything!

might also be the heat shield on the catalytic converter has come loose and is rattling around.

IMO, it should be ok to use that other Dodge Dakota muffler on your jeep.

The cat will rattle when you turn it off if it is bad.