Hi James. The noise you are referring to is called "injector crackle"
The reason for this is the increase in fuel (a bit like a choke on a petrol engine) to help with the starting and running when cold. The injector pump has a wax pellet that melts to return to normal running. This is your 30 second period. The colder the ambient temperature, the longer the pellet takes to melt, the longer the crackle will continue. There is another scenario where the injectors "dribble" due to wear, but this is normally accompanied by intermittent crackle at idle. If the vehicle is high mileage 80,000+ it wouldn't hurt to get them checked anyway, you could save yourself some mileage costs if they are worn too much. So to answer your question and if you have no running or economy concerns, the noise is fairly normal in moderation. ie not overly loud. Good luck.
Paul
February 2008
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