[Jim Vander Wal]

My $0.02.
Joey.S brought the potential of a rod bearing. Let's follow that.
If pulling a plug wire eliminated the ignition (kaboom) in #7, perhaps that stopped the rod from pushing down on the crank journal - the tick. Now without the ignition in the #7 cylinder the crank is pulling the rod rather than the normal of having the piston push on the rod.
Hope this makes sense, sorta does to me. Otherwise just ignore my WAG.
I'd look at a lot before pulling the pan, yup a PITA with the SPF/Canton combination. Been there done that, I didn't like it either.
Jim