Weird Rattling

I have been noticing a rattling noise that would last no more then 1-2 seconds on start up. Only when is hot outside and the truck been sitting for few hours. Doesn’t do it in the morning or when it’s cold outside. Seems to be coming form the engine but couldn’t pin-point it.
Any ideas?
Thanks

 

That's a hard one. Metal rattle? Best is if you anticipate it, have someone listen with the hood open while you start it.
A video may or may not help, but I usually try to grab one to share if I'm just stumped. Good luck man.

 

I can hear from inside. Tried to let someone start it while I am looking at the engine bay and couldn’t hear it. Dealership couldn’t hear it as well and the tech said it is possibly due to the oil not reached to top of the engine heads yet. But wouldn’t do it in the morning or when when it’s cold outside? I will try to get a video.
Thanks