Hi, When I start my truck after it's been sitting for a few (or more) hours, I get a strange noise coming from under my Timing Belt Cover, on the right side about 8 inches down from the top apex of the Cover.

The noise sounds like something metal tapping plastic matched to the current RPM's. You can also feel the Cover in that exact spot and it feels like something is hitting it, but both they completely go away after a few minutes of running.

This is where I am stumped. The engine runs great and smooth, even when it's cold and making said noise. It fires right up and doesn't "diesel" when I kill it. It shows no signs of bad timing whatsoever. I just took it through Emissions in WA the other day and passed with better than flying colors.

So that leads me to believe that that is nothing wrong with my Belt or any of the pulleys.

So what is this mystery noise?

 

Maybe a bad lifter. It is hard to diagnose a noise problem over the internet.

 

The sound is coming from below the Head. It is not a Knock or Ping. Take a piece of metal and tap a piece of plastic at about 800 times a minute. That is what it sounds like.

The only thing I can think of due to the location of the sound is that my timing belt is loose and hitting the timing cover, but there is no evidence of bad timing due to a loose/damaged belt.

 

Okay, it happens when the engine is cold but goes away after it warms up. Don't know about the 4-banger in Dakotas, but in other 4 and 6 cylinder engines there is a timing chain/belt tensioner that operates off of oil pressure. It keeps the belt/chain tension where it should be. If the four banger has a tensioner like this, it means your belt/chain tensioner isn't doing it's job when the engine is cold, but as engine temp/oil pressure come up it kicks in and goes to work. Eventually this will weaken the belt/chain and it will break...no wueno por nada...bad, very bad.
Or, as Crazy says, it might just be a lazy lifter that is rattling until engne temp/oil pressure come up. More than once I have used a wooden dowl or length of rubber hose like a doctor's stethoscope to track down a noise under the hood...just keep it and your head away from moving parts.