Noisy engine when it is cold

I have a 2001 Dodge caravan. When I start engine in the norning, it very noisy engine about 10 second depend on the weather it is more noise when it colder and less noise when worm weather, It will make noise only one time a day. After started engine about 30 second I turn of and start it again now it sound normal ( I living in San francisco) I learn and have some experienced car repair, I try to find and think what cause that noise for many months and I still no anser.
what I know is weird noise came from top engine, and sound like from camshaft bearing but I am not shure Please, give me an idea what cause that noise. I warry my engine will break some day.
What it cause rpm. Too high when start cold engine and how to fix it. Thank you for your time.