With the engine running at idle, pull spark plug wires off the coilpack one at a time. See if the "knock" goes away when the combustion is removed from the ticking cylinder. As long as you pull them off the coilpack quickly and place them back quickly you will not get shocked. trust me.
If the sound does go away with a wire pulled, make a note of which cylinder it is, as, it might be a rod bearing, and it is knocking when the combustion happens.
Also note if the ticking goes in rhythm with the arcing spark you created. If it does, it is valve train related.
The "rhythm" of the knocking seems to be "half speed" of the engine to me, which would indicate a lifter-rocker arm-pushrod problem. A worn rod bearing usually taps very fast. Keep in mind, the engine rotates 2 times the speed of the camshaft, so valvetrain noises "knock" at a slower rate than a rod bearing.
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a bent push rod, collapsed lifter, broken rocker arm, or sticking valve will cause a huge amount of slop, which can sound like someone trying to escape from inside the engine with a hammer. Heck, it could even be a huge amount of carbon buildup.
A little trans fluid sucked into the intake via a vacuum line, left to sit overnite followed by A seafoam treatment might do wonders for this.
I had a friend who broke down and bawled when his prize chevy truck made a knocking noise. He swore it was a rod.
alocal mechanic ran some trans fluid into it, let it sit overnight and seafomed it. There must have been a carbon deposit in a valve seat which did not allow the valve to completely close, causing a knock due to the slop in the rocker arm-pushrod, because after burning out the gunk the noise went away. He still drives this truck to this day.