That rattling got me, too...

Turns out to be just the platinum material breaking down - but i sure was having a blast with the extra torque provided by the lessened restriction!

Bad idea! Rattling got to be so much that the pieces turned into tennis balls rolling in and out of the remaining exhaust train...

Result? Everytime i took off i was bogged down due to a clogged exhaust - slammed on the break and all was well till i had to take off again

Crawl under car when it's cooled off - slam the outer side of your fist on the main body of the cat and listen to the exhaust - rattle sound to be internal?

Check all the bolt/clamps then try it again

Still rattling? Replace the cat and be prepared to remove the rest of the exhaust to retrieve the Gremlins the old cat gave birth to - lol

Tim