It turned out to be a bolt that had snapped so the clip that held the centre pipe to the manifold had come away.
18 years of wear and tear.
At first it looked like I would need a new clip but with some Burrows magic and a hammer I got it out.
Then it came to fitting it. I replaced the broken bolt with a shiny new one and enlisted the services of the Ramus' to tighten the clip as I pushed the exhaust back together.
Now its sounds very quite.