Given the history with the harmonic balancer and flex plate,i think it warrants some more diagnosis.
You can use a long solid object (long screwdriver or long extension bar) to listen to the engine and pinpoint the source of a noise.
Wrap your fist around the screwdriver with thumb at the top. Place pointy end of screwdriver against the engine. Place ear on curled thumb/fist.
This amplifies sound directly into your ear.
Now move the pointy end of the screwdriver to various places in the engine block, head, injection pump etc
You can pinpoint noises very close to the source by listen to changes in intensity of noise as you shift the screwdriver to different points on the engine.
If nothing stands out as being markedly different, maybe nothing to worry about. If you find sound is more intense/sharper in or around a specific location, you mace have found a problem that should be investigated.
with attention to detail, you can hear individual valves open/ close, individual injectors crack open, knock/tap etc of individual cylinders firing.
You can't get direct contact to rods, but placing screwdriver life in the block in line with each cylinder, you will hear noise transmitted through the block and screwdriver.
Also, drop the oil and look for glitter.
Have a used oil sample sent out for analysis (Blackstone Labsc etc), see if there's elevated bearing metals present in the sample.
