[Farrell In Vancouver]

Long shot in the dark?
Have you tried eyeballing it in the dark?
Possible shorting you cannot see in the light?
You mentioned changing the high tension lead as "it was a little loose"
Sometimes with a leaky boot, you can build up a carbon track on the tower of the coil or across the distributor cap. When conditions are right the energy goes to ground on the easiest path. This would give you a fairly good charge of unburnt fuel in the pipe and a neighbor waking backfire.
Of course you've changed the coil out, but have you had a good look at the cap?
Good luck in the hunt, I hope you find it soon!