lol Been a few threads about this lately.
My clicking/ticking/tapping or however you choose to describe it at only idle speeds is now gone, I switched to Mopar oil filters and use Lucas Oil Stabilizer with good brand name oil.
The Lucas is great stuff, it's very very thick, stick like honey so when the engine is off it clings to prevent dry starts, as well being so thick is raises the oil pressure.
Be aware though, I use to run 1L of it in my Ram's V8 all the time and in those -40C nights, with a weak battery she turns hard when starting. :P
As for the noise, no one seems to know, just theory's. Some that don't know these motors say bad lifters, other said loose or wore timing components. It's only present at idle so I don't hold to much worry.