I have a rather loud clack or ticking noise at idle that I seem to remember reading somewhere might be coming from the oil pump drive shaft. Any conformation on that theory? If so, what is the fix other than replacing the shaft? Timing chain, tensioner and gears have been changed. Valves are adjusted properly and I'm confident it's not coming from the valve train. The noise is not heavy enough to be main or rod bearings.Pistons and liners are new . Engine runs strong and sounds great above idle. Thanks KSD