Tapping noise

[Sspangler13]

Hello, I am looking for some help diagnosing a tinny tapping noise from my engine. The noise started one day after driving for an hour or so, non-rhythmic and seems to be coming from front driver side. I bought this FFR MK3 from the second owner so he did not know much about the engine build. Here is what I do know. Engine is from a 89 GT Mustang, has about 9800 miles since build. New crank, bearings, rings oil pump, forged Pistons, Comp cams Gordon Levy cam profile( whatever that is), edelbrock performer rpm intake, edelbrock aluminum heads with 202 valves, edelbrock 600 carb, and MSD pro billit distributor. I have ran the motor and tried to locate noise with a stethoscope, no help, pulled the oil pan and checked what can be seen inside all looked good. Ran engine with no valve covers and all looks good, all Valves opening and closing well. There is no engine miss and seems to have all the power it did before the noise started. Have been told may be a sticking lifter, but shouldn't I be able to detect it with one of my methods tried so far? I can replace anything it needs but my diagnostic skills are lacking. Any ideas are most welcome. Thank you.
Sean