I know this thread is old, but I have the exact same problem. After sitting more than ~10 hours I have the cold start clank. It lasts until the engine is mostly warmed up. As far as I can tell its just a single lifter that is having problems pumping up. I'm using rotella t 15w-40. You are very right, its very embarresing listening to the engine clank away.
Should I attempt to replace the single lifter, or just accept a bit of clanking?
