I have a 300TD that I've owned for a couple/few years. The whole time I've run it, it has had a tapping noise that is quite noticeable when cold that sounds like a valve. It sounds just like a car with hydraulic lifters when one of the lifters doesn't work. Tap, tap, tap. The noise is very intermittent, tho. Usually with a bit of a drive it can go away entirely or come and go. All valves have been adjusted twice in the time I've owned it. All the injectors have been rebuilt once with new nozzles and checked another time. I'm thinking my next step should be to run it with all the accessory belts off to see if the noise goes away. Any other thoughts?