Howdy fellas, hope everyone's having a good day.

Had a question for you more knowledgable folks on an issue I'm seeming to have on a Ranger I very recently acquired. It's a 2001 with the 4.0 SOHC V6 and the 5R55E transmission. Got a lot of plans for modifying it, but I need to fix a few issues I've began to notice.

My issue is that there's a rattle going on that sounds like it's coming from the engine bay though it can also be heard from under the truck right around or above the cats. It sounds more like it's coming from the passenger side than the driver side from down under but from up top it sounds like it could be coming from the driver side.

The rattle sounds like a very loud metallic-like ticking. It doesn't necessarily happen all the time; sometimes on a cold start, sometimes when it's at operating temperatures.
The motor was rebuilt so i'd like to get the timing chain guides out of the equation but I'm not entirely certain yet.

When I rev the engine a little bit the rattling goes away and after a few minutes it slowly comes back. Slowly meaning that it starts soft and progressively gets louder.

Any advice will be greatly appreciated!

And here's a picture of her!