Ok when my engine is running, it has a a rattle can noise in the background.
The engine rungs great but when I rev or drive it sounds like something is loose, rattling.
I search under the car, nothing is loose, cat, muffler, etc etc.
Has anyone else had this problem? Also I found out this is not a California car, which explains some of the rust on the manifold bolts. One more thing, I remove my seats to clean my carpet, and the metal plate under the seat had surface rust, is this normal or was my car use as a Submarine in some lake? LOL

 

Probably a heat shield that's loose or rattling against the exhaust.

Don't cats also rattle when they are going bad?

 

They do, the beds inside the cat break apart when they are going bad it rattles around inside the cat and teh rest of the exhaust. Check the last O2 sensor (after the cat) to make sure that the cat is working fine. The O2 sensor should read 0V i think (should be reading lean mixture)

 

Thanks for that info. I checked the heat sheild and it was secure, so now I will check the cat.
Actually I have seen them on ebay for 40+ dollars, are those any good? Reason im asking, I might as well change the whole exhaust seeing that I have 135000 miles on the car and its never been changed.