Damp weather and engine noise

My 2011 Honda Civic makes a grinding / squeeking sort of noise when I start it after it has been sitting out in the rain - either for several hours or overnight. The noise seems a bit like the noise when you crank the car but the engine doesn’t start. It happens after rain or a snow, so it would seem that moisture is getting into a place it shouldn’t. The dealship checked it out and couldn’t find anything wrong or anything that would prevent it from starting. They also told me that this noise might well go away after the first oil change - that the additives in the oil now are suppose to help seal things. Any advice or suggestions on what to have check would be greatly appreciated.

Check the weather report and offer to leave it overnight while it rains(be sure to ask for a loaner in case you need to use a car). Let them look at it after it’s been sitting in the rain on their lot and they might be better able to diagnose it.
What they told you is standard fare for problems they can’t really figure out.