Rep Power: 0

I'm getting what sounds like a heat shield vibrating when the car's cold and idles a bit faster for the first minute or two on a cold morning. It's mostly when I'm backing out of the garage and the engine's cold. After it idles for about a minute after that it stops. Any ideas? I was under the car yesterday for the first oil change and the only thing I can figure it could be is one of the heat shields attached to the exhaust pipe. Anyone else experienced this? I'm sure there's no possible way the dealer service dept will reproduce it unless I leave it there overnight, but it'll likely end up being a big waste of time.