The way you said it's bad right when you start it and it quiets down as the idle comes down makes me think 99% that it's lifters, but that's a good point, those egr tubes and especially the piece that goes between it and the manifold to get real nasty and can get rust holes and crack.

 

I heard adding Lucas Oil Additive to your engine when changing the oil helps silence the tick down a little bit, im about to try it tomorow when i change my oil