This rattle has been going on for a little while at low revs (especially when reversing). Finally thought about it seriously yesterday and found the rattle. It's in the exhaust system. And it's in the exhaust box/muffler/chamber that sits directly underneath the driver. I assume it's the first chamber after the engine.

What does this chamber do? Is it critical or just merely important?

Obviously something is broken but whatever it is doesn't seem to be impeding performance. Replacing it will cost money but the amount depends on whether I can replace it with a simple steel tube or whether I need the bespoke part.

Comments?