Ratling noise

We can't hear it. You're going to have to be a little more specific as to what it sounds like, when it does it, and what the question is.

Much more informative. Which engine do you have? Still don't know what it sounds like or when it does it.

I have an '88 Grand Caravan daily driver with the 3.0L engine that has been making a loud clicking sound for the last eight years, but only at idle. It runs fine but people get out of my way in parking lots.

I also have an '89 Grand Voyager 3.0L that had loud knocking and pulsing oil pressure from a spun crankshaft bearing and damaged crankshaft. It needed a total engine rebuild. I suspect your problem is somewhere between those two extremes.

Good clues. Start with removing the serpentine belt to see if the noise is still there. If it is not, the more likely suspects would be the water pump in the front, bottom, and the harmonic balancer that drives the belt. Either of those will feel loose once the belt tension is removed.

If the spring-loaded tensioner is worn it can bounce up and down and make a rattling noise. It should move freely and smoothly as you pull on it with a 15mm wrench.