I have had an annoying tinny type rattle on the exhaust of my Astra-J now for a few weeks that stopped if I held my foot against the side of the end of the exhaust.
I finally managed to take a look yesterday, fearing it could be loose baffles, or a broken bracket.

The end of the exhaust has a chrome tip attached to it. It turned out that loose chippings had somehow managed to enter from under the car into the gap between the chrome tip and the exhaust pipe and were rattling around in the cavity!!

Half hour later, after ferreting around with a plastic cable tie and some stiff wire, I managed to extract approx. 12 chippings, and a small twig from the gap.

Result! The annoying rattle has gone