GrandJP for $450 you should be able to get a high flow stainless steel jobbie. Give
Liverpool Exhaust a call, that's where i got my exhaust done and so did Cpage. He recommended them to me and i'm happy with their price and the job that they did.
Inside a cat there's a ceramic block, and if broken apart will sound exactly like you're describing.
It's wierd because they rely on heat to function as intended but can break apart if the exhaust temperature gets
too hot. It can also break apart if it cops a big enough hit offraod.
Then it could just be one of those things that happens for no apparent reason, call it unlucky.
Here's some info on them
howstuffworks.com
Cheers.