Slight Knocking like Noise

Hello, I have a 95 4x4 5spd with the 4cyl 3rz. I recently had an issue where the harmonic balancer bolt came loose. It did not appear to do any major damage, so we replaced the balancer, smoothed out the crankshaft, and fixed the problem. We also replaced the oil pump while we were in there(it had an aftermarket on it, but we broke it putting the pulley on and put the original back on, but with the gears from the aftermarket).
The truck ran perfectly fine but when it got up to temperature, the oil light would come on at idle. We solved this temporarily by adding thicker oil, but we then went ahead and put an OEM Toyota oil pump on and put the original(new oil, correct thickness) synthetic oil back in it. The oil pressure is fine and it runs back to normal, however now when the motor is hot and in gear, running it lightly on the throttle around 2500-3000 rpm’s causing a slight knocking like sound. My dad says it is the valves pinging, and he may be right but I don’t know. The noise goes away when heavy on the gas or very softly on the gas.

What could be causing this?

(I also installed an o2 sensor sim that fixed my CEL and caused some rattling on the cat shield, there might be a chance that it is hitting something like the cat shield and making that noise).