Hey guys noticed my car sounds kinda like a diesel at hot idle. What could cause this? I also noticed that my header has a crack in it...can this cause it to sound like that??

 

The crack in the header could certainly be the cause.
You've got a ticking, chugging, rattle right?
With a little luck you may be able to get it temporarily fixed by a skilled welder, but he fix probably wont last long.
Start saving for a header, it's in your immediate future.