Toyota 4WD Surf Owners

I posted this on another Surf site looking for some help, figured I'd share here too.

A few weeks back, seemingly overnight, my 1991 Surf SSR-G (2LTE) became much louder while running.

So far it is difficult to narrow down, but sounds closer to the top of the engine. I put a screwdriver to my ear and poked around but could not pinpoint it.
I haven't had much time to dig into it, so the truck has sat mostly parked, while I drove the rest of the fleet.

The few times I have started it up, I've noticed the sound is gone while the engine is cold. After a short drive (2 km to work), the sound is back. The truck is now at my workplace so I can use the shop to begin sorting it out.

Most notably, the truck runs exactly the same as normal. No extra smoke, no loss of power. Just noise. This makes it hard to believe that the timing belt has slipped or otherwise went out.

Just looking for any guidance as to what I should check instead of ripping into it blindly. So far my plans are:

Run the truck, crack open the injector lines one at a time
Check Fuel pump timing
Pull timing cover and inspect components
Pull Valve cover and inspect valves/clearance (I've never done a valve job before)

Recently, the truck has had some work done:

- Front main seal went, replaced it and the timing belt (water pump and idlers are still fairly new)
- Resistor mod on fuel pump (could a bad resistor cause this knocking sound?)
-Idler arm, tie rod ends, alignment (not engine related)

Here is a short clip of what it sounds like:

https://youtu.be/kzMNqbH5HBc


Any wisdom out there? Thanks for reading!