Most common source of internal exhaust rattle?
 

I have a 2002 "S" model. I have an internal exhaust rattle that only starts when the exhaust is hot. I checked the usual source, the shields on the cats, and it's not them. I've gotten under the car when it's hot and listened but I can't zero in on it. It's relatively quiet at idle, it's fairly loud on hard acceleration and definitely at its worst on deceleration. Is it typically the cats on the exhaust manifolds, the secondary cats, or the muffler that usually cause this?

My 98 base also had an exhaust rattle. This was with an aftermarket Dansk sport exhaust. It only happened when the exhaust was cold. It turned out that the perforated "shields" in the exhaust tips (what is their purpose anyway?) were loose. With some wire and the Permatex muffler repair paste I was able to secure them and the rattle hasn't returned since. I am not familiar with the S muffler but you may want to tap the various components of the exhaust system including the clamps with a rubber mallet with the car off to see where there is a loose part

I've tried tapping it, etc - no way to reproduce. I think I just have to start replacing parts until it disappears. Just looking for the most common place to start. Anyone?

Factory exhaust, or aftermarket?

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Mine was rattling/buzzing when cold. Found it was inside the muffler and it was likely a baffle that broke loose. I bought a low mileage take off on Ebay and the problem when away. I could reproduce it by banging in the underbelly of the muffler.

Cats can definitely rattle. The interior melts a bit and they get noisy. If that is the case, there could be some other issue as well causing the cat/s to overheat. I would expect it would be replicable with a hammer test though. Can you pinpoint the side? Maybe start the car drive it a bit, get it hot and crawl under with someone at the throttle. Might be able to pinpoint that way.

If you are just going to start replacing parts I would start with rear cat delete pipes . You will eliminate one pair of cats that could be your source of rattle and you'll free up the exhaust a little bit so a win/win . Assuming you have eliminated any heat shielding as the rattle source you would then be down to front cats or the muffler/exhaust tips .