I have a new 08 Civic EX Coupe Auto with about 3800 miles.
I am getting a rattle when the car idles fast for the first few minutes after a cold start. It sounds like a heat shield or something. I will take a look when I give the car it's first oil change because the dealer will never "reproduce" the problem unless I leave it there overnight and then it will end up being a complete waste of time and energy anyway. The rattle only happens when I put the car in reverse or drive in the few minutes it idles faster than normal when it's cold. Has anyone else experienced this? The only time it ever does it is when it's cold in the morning 25degrees or below. I'm not too worried, just curious if anyone else has heard this rattle when cold. It's pretty much done it since it has gotten colder here in the last month or so. Thanks.

I have been going through similar issues myself with my 98 dx. It's the worst when it is very cold outside, but it does get better when the exhaust is up to its normal operating temperature. Unfortunately I don't have a solution to it yet...

i heard this myself on a few new civics and seemed to be coming from the rear like the exhaust pipe was hitting something, maybe the rear sway bar. might wanna check that first.