I think the system i have is an aftermarket one by the looks of it.....I haven't had it on my car, i just bought it as a spare, but at the moment i need the money! Being a student, repairing the Omega headgasket failure, buying a hyundai run-about for the time being, and working at Halfords means that my bank balance really isn't very healthy at the moment!!! 

The issue with the gasket sounded just like an exhaust blow.

A cracked manifold or a manifold gasket will sound like a tapping on the V6's.

Just get under the car with the engine running and feel up aound the downpipe's to check if you can feel it blowing.

Do it with the car cold though, as you will touch the exhaust doing this, and they get hot enough to melt human bone!

jesus.. i was thinking id fork out for the section of exhaust i need myself but if thats the price the DOE will be getting a nice letter containing pics and a complaint about how a speed hump has shattered part of the internals of one of my cats. the rattle is doing my head in.