Chattering noise.. search narrowed down.

I've checked the plugs and wires and they are all ok. Swapped them all around and the noise is still there. I will change the exhaust manifold gasket next although it is a new Felpro one with less than 200 miles on it. I've checked it visually and can see nothing wrong. This chattering noise under load is loud enough to be heard outside the car.

The noise just sound sounds too chattery for a manifold leak but I would like to be proved wrong. I had a 70 Cuda with a leaking manifold and although that ticked away you could hear it all the time.

I'll be away for a while on business so look forward to any replies.

Cheers guys.