I have a really bad rattle. It is from inside the cat. I need to replace it with a diffrent one. But i need to find out what size. I want a magnaflow universal one. no direct fit way to much $$$$$. can any one help with the size? I have a 98 chevy blazer LS 4x4 with 4.3L all stock. any help would be nice

 

Not sure of the size but, are you sure the rattle is from inside the cat and not just a heat shield.

 

2.5" in/out.