This just started yesterday on cold start and happened again this morning and this evening always after sitting for hours. I would call it a chatter sound, very distinct and only on the first start. Never heard it before. Have 97K on car, will be changing the plugs soon. Once it is warm the sound is not there on starts. It is only when starting, sounds fine once running. What would only be noisy when cold like this? Timing chain? Valves? I'm going to let others with a better sense of engines than me (my son and his friend who are mechanics) listen to it and see what they think. But it needs to be cold. Never heard such a sound on my Hondas which makes me think it may be the chain. Funny how it just came out of no where.