I had this EXACT same noise on startup just a few weeks ago, My car was down for 5-6 months since end of july and I did work plus had my top end sent out. I had this EXACT clatter. I have some vids but Im at work and I can upload them and post when im at home on wifi.
Long story short.. idled for a few mins.. gave a tiny bit of rpm to increase oil pressure.. clacking tapered down and then disappeared. A little bit of run time later it was breaking new acceleration numbers on the g-tech
