go back to the distributor cap and look real close inside it and look at the points from the electrodes to the center tap and check for any cracks. Use a bright light and even get a magnifying glass so you can get a good look. If there are any they will show up either by being able to see them or you can see the carbon trails the arcing leaves behind. The spark will follow these cracks towards the center pole or even across other adjacent cylinders if the cracks connect to them.
Because you disconnected the #2 plug and the problem calmed down tells me you are having a cross fire issue causing that cylinder to fire out of time.
At least that's what it sounds like to me.