I,ve recentrly replace my oil to 10w30 mobil 1 and every time a leave my car in the sun for 4 or 4 hour and i strat my engine it make a small valve noise. this didnt hapend with my old brand of oil motul 5w40 is this dou tooil change or my car has aproblem the noise is only for 1sec

my car c230k 2002 coupe

 

Mobil 1 will not cause you a problem. Heck, it'll save you problems down the road.
Your old 5W40 was thicker than 10W30 so it may have masked an existing problem. Now that your using a lighter weight oil it is exposing a problem.

Make sure you have ENOUGHOil.
If you have sticky valves you can put in some product to
get rid of sticking valves.