I have a mild amount of what appears to be smoke coming out from under the hood. I noticed it yesterday when I was parked with the engine running while it was raining, and thought it was just from the cold rain on the heat of the hood. Then I noticed it again today while it was sunny... it's not a lot, and it's not thick smoke. My question is, what could be causing this? My temperature gauge hasn't budged, and none of the engine warning lights are coming on to signal a problem.