94' Cutlass Supreme Exhaust

Firstly I have a 94' Oldsmobile Cutlass Supreme 2 Door 3.1 V6

Was driving to the store 2 days ago, and I noticed this sound coming from the back. A rumbling sound.

I at first thought it was the breaks. I left it on so listed to the end of the exhaust, which I could slight hear the rumbling noise. It honestly doesn't seem like there is a hole in it, more like it could be clogged up?

I don't really know much about the exhaust system, other then the fact the Cat can get clogged. Is it possible the Cat's clogged and making the noise all the way at the end? The muffler has kinda of a erratic shake to it, if that helps.

Is it possible to just replace certain parts of the exhaust system? (Legally)

I come to you all, as I want to go at this in the right direction. Try to spend the less money and right way of fixing it.

Thanks, and sorry for the long type up, just wanted to give all the facts I could.