So yesterday I noticed kind of a deep rattling sound coming from under the car on the passenger side. It seems to be coming from near the muffler/cats. It makes noises both when I'm at a stop or driving. Any ideas what could cause this?
I would really appreciate some help...

 

just a WAG but have you considered the exhaust system?

 

Yeah I thought it was something in the exhaust system... but I want to know what exactly could cause that... How can I test to see what it is? And also I'd like to repair it myself but I would like to know if it's too big of a job for me and if I'll need to take the car in.

 

Yeah I have the same think that rattles when I'm in the parking lot. Its a rusted old cat and a hole in the exhaust. Some JB weld fixed it for two months then it came back