Annoying rattling sounds, 94 grand am GT

[Krono353]

Ok, here's the situation. I have a 94 grand am gt. Recently it's started making this rattling sound. It's a manual so I usually shift around 3000 rpms but before that I shifted at 2500 (it was a friend that told me 3000 is safer for the engine itself). Usually around the 3000 rpms there is this rattling noise somewhere. The noise has become more recent since I changed when I shift. It sounded like it was somewhere in the back, but due to the rust underneath one of my mufflers actually fell off. So the sound is more like it's up front somewhere. I think it may be the other muffler or maybe something broke inside the exhaust somewhere. My mother's civic had something broke inside it's muffler and made a very similar sound. Another friend told me that it may be the transmission. I'm hoping that isn't it though. I've checked the fluid and added a little a couple months ago. I'm going to get this checked but I'm hoping for some input to hopefully put my worried mind at ease. Any questions feel free to ask, I do appreciate the help I may receive.

[GTP Dad]

The best thing to do would be to crawl under the car and look for loose items. Sometimes heat shields on exhaust manifolds and catalytic converters come loose and make noise. This would be the place to start. Also look at the exhaust system as it is always a source of rattles. Finally there is a possibility that your cat is going bad. If they melt down and break up into chunks that will cause a rattle that you may be able to hear especially at higher RPM's.

[Krono353]

Alright thank you. I just had a buddy of mine put a new muffler on. More work is going to be done with weekend. He said the sound does sound like it's coming from the cat. So that will probably be the next move. But thanks again, I really do appreciate the input.