They are a bit 'clackity' in Mopars. My best guess as to why is that they are essentially a 'scaled up' .904 based on profiles obviously designed for the much more popular SBC which has Much Lighter valvetrain mass. Weigh the valves, lifters, pushrods, springs and retainers side by side and it's pretty easy to figure out where the clatter from the faster ramps is coming from.