The morning after a sprited 180mile drive I was stuck in a queue of traffic while the engine was still very cold. I could hear an intermittent crackling sound, very loud, like frying eggs or a louder version of the sound you get when the car is cooling down. Remember, this was within 60 secs of startup. The noise was so loud that even the guy in front started looking around. However, once warm, the noise ceased and I haven't heard it since. Apart from the local 'boys' putting gun caps on the manifold, any ideas as to what this could be???

Funny you should mention this, since on Sunday I had the bonnet up and was testing some driving lamps. I started the engine and while it was idling I got this crackling and pinging noise from the lower area of the bay.

I looked down and touched the heatshield covering the exhaust X-over pipe which runs across the front of the engine and could feel the noise coming from the shield. As it heated up the noise stopped. I think you will find it's the classic Japanese tin-plate syndrome where the heat shielding expands and moves about making the noise.