When I first start the engine and its cold the noise is very slight, however after driving and engine is warm the grinding is much noisier. Can be noticed from the cab of the truck, with window down.

The engine idle's fine, no noticeable power loss or effect on driving, no performance issues. The oil has no added colors, and is at full level. Its an automatic transmission and there are no issues with gear changing.

The grinding is not uniform. I thought it might have something to do with the fan, so with the truck off, I checked to see if it was the fan clutch possibly, and the fan spins without little resistance. I don't think that's normal. Any idea's?

I think it might be my timing chain, I've done some reading and since I have 240k km's on the engine, its about time for a 22re's timing chain to act up, and the rattle of the engine, even though not terrible, is coming from inside the engine. Good guess?