My 02 Ford Ranger 2.5 TD has developed a metalic rattle on startup. It seems to come from the front of the engine and gets less as the engine warms up. Once it's warm I can't hear it. It started as I got to France and as I was on my way to Spain I hoped it wasn't too serious. That was 4000 miles ago and I've just got back. I wonder if it's the valve gear, does anyone have any ideas?