Arcing across coil terminals

Got here late. I tried to read everything may have missed something. As others say visual inspection, and new does not aways mean good. Really difficult to see tracking .... you also have to know what it looks like. It has metalic glint, may need bright light and right angle. Once tracked, never quite as good, even with cleaning. Wear nitrile gloves, sweat is a good conductor. Especially when handling plugs,cap, rotor, cables.
Use an Ohm meter, go from cap terminal, all the way to plug tip. I do that when installing new wires. Longer wires will have more resistance, but all shold be in ballpark. Trim excess condutor tail past, where terminals crimp on. Do not cut into sheath insulation. Plug wires usually need work prior to install.
Resistance plugs are common used with COP, not needed with resistance cables.... using then may increase arc over.
With the popping noise, how often? One of 8, all 8, 2 together followed by delay? Knowing that helps diagnose.