I have a bad feeling we have a loose or damaged connecting rod bearing. We recently finished the rebuild on this truck and it has not made any noise until now. Recently, this engine has begun making a light knocking noise but only under a load. At idle, it sounds just fine. Maybe a slight tap but it's hard to hear. I thought it may be the flywheel bolts loosening up or something but after listening tonight, I don't think so.

Any suggestions? It looks impossible to get the pan off with the engine in the truck and they certainly did not make this thing easy to get out.

My son also said there was a sound that was like the fan hitting on something from time to time, but I did not hear that at all.

 

What oil PSI iS it holding? Yes I think you are right. Time for crank and rod bearings.