I've noticed that my 06 Buick Lacrosse makes a light rattling noise upon start up when the engine is cool. This lasts for about 5-10 minutes until the engine warms up and happens whether it is in idle or is being driven. The noise disappears completely once engine is warm. This happens everyday and has been happening for the last month. It does not seem to matter what the temperature is since it has been 80 some days and in the 40's these last few days upon start up. No indicator warning lights go on and the car drives smooth so not real sure if I should get it checked out or not. I have checked other websites and read that there is a piece of plastic that is being hit by a fan and there is nothing that can be done except getting that piece of plastic cut so that the noise disappears. Any advice?