Coolant loss could be the bypass hose in the intake, I blew that one out and it took me forever to fix.

As for rattling.. Haven't got a clue...

 

Thanks for the info guys. I gotta funny feeling it's the plenum. I watched a YouTube bid on replacing the plenum. When he took the intake off there was coolant sitting in slots next to the gaskets. The only doubts I have is when I checked in the throttle body there was very little oil. And my truck doesnt burn oil at all. I've read if you have a bad plenum it eats oil up. As for coolant disappearing, I checked at thermostat, timing cover, overflow is not cracked. No coolant on pass floor. And it doesn't smoke. I'm gonna change the plugs wires cap and rotor. See if I get any power outta this dog and if pinging stops. I appreciate everything guys. Thanks for all the replies it's been helpful.

 

All you're advocating is replacing a bunch of parts rather than properly diagnosing the problem

How is needlessly spending money "cheap and easy"?

 

Nope, VW, have to disagree. He just bought the truck with 130 k miles. Probably has no idea when plugs, wires, etc, were replaced. I'm advocating taking care of routine maintenance issues before tearing into the plenum.

 

The OP needs remove the TB and look around with a light and a small mirror. Looking down the plates is worthless. And since he'll have the air cleaner housing off to do the cap and rotor, only a few more steps and he can check the plenum for real.