Thanks everyone for the replies, calmed me down quite a lot just to have a general idea of what to look into. I did a vacuum leak test and found nothing major (just a loose hose, since been replaced.)
As for Eric’s answer, my father actually thought the same thing prior so I was planning on getting under there and tearing my exhaust apart to see the damage firsthand. I’m in the process of acquiring a new cat, though the rattling is going on pretty deep into the system (I’m pretty sure there’s some debris sitting in the resonator) so I might as well rip out the entire exhaust and clear that up.
Another question, are there any components that I may need to inspect for damage or readjust this early into the problem?
Again, thanks a lot everyone, really helps to have even the slightest idea of what’s going on.