Just did my oil today and checked my plugs, no oil fouling them, and started the car up, put my thumb on each spark plug wire cap, wires 1,3,4 are feeling stable, yet when I put my thumb on plug wire 2, I feel a steady thump, or knock, no audible sound in engine, or during startup, reving up, or driving, engine runs completely fine for 175km, I read a post from before, someone felt the same exact thing, but the thread never came to a conclusion, so I'm looking for more information, and have yet to find any information to if it is normal operational feelings, or something going wrong? Bad plugs? Rod knock? Bad plug wires? In the picture is plug 1 (right) plug 2 the "thumper"(left)