1998 Ford Ranger Engine clatter

Is it a 4.0 SOHC or OHV. 98 should be a SOHC which means it may be the timing chain guides. They're plastic and break if they flop around too much. Since the chain tensioner is oil fed, for some fluke reason, it may have emptied and not put enough tension on the chain during start-up. Or the tensioner itself could be bad. Let me know if you need anything.

Is it coming from the top side or from the bottom?

If I had to take a stab at it without hearing it, I would guess that it is valve chatter. My guess is the lifters are tight now because of the new oil. What weight oil did you use?

Even though 10w30 is what you may have always used, the higher viscosity oil may be taking it's toll on the engine. All the parts are designed within certain parameters and your engine was designed for 5w30. The thicker oil may have damaged the lifters to where they are not pumped up enough and you now have loose rockers.