Here's what happened: I was beginning to notice a rattle coming from front/middle of the car when starting and lightly depressing the gas. Took it to NTB who said that Cat's honeycomb center had melted somewhat and was freely moving within the cat's case causing the rattle. They didn't take it off to look but they think that's what happened. Can it or are they trying to scam me? High flow cat time?

 

Cats can and do go bad, but usually they just get clogged up and don't break apart internally, as far as I've seen.

 

check all the exhaust bolts and hangers. When things are cold, they don't fit together as tightly, so that would explain why the problem only happens when first started. If something is loose in the exhaust it will be more noticable at startup.

 

one of your exhaust hangers is rusted. probably your b-pipe is hitting the metal bar support under the rear seat.

 

i had that happen on to a beretta i owned, shot some honeycombs out the exhaust like it was cool. replace your cat asap, keep an eye on your ecu too

 

yes that can most deffinatly happen. you can easily test if that is the problem too by lightly tapping the cat with a rubber mallet. if you hear anything rattling than its time for a new one.

 

you could take the cat off and see it theres anything moving around in it.

 

make sure that's what it is for sure (that the cat is out). I have been told that i need a whole new catback when it was just a hanger i'd suggest inspecting the cat yourself to save yourself some money, if it's just a hanger that's like $5 for the welding