i got a 2004 f-250 6.0 diesel. Whenever i start the truck it makes a noise like if chunks of metal were twirling around. It does it and then the truck starts and sometimes it won't do it and sometimes it will. What could it be.

 

Loose starter bolts - check that first. Can create horrible sounds and will fry the ring gear, eventually.

 

It could also be a pulley, either idler or tensioner