I'm pretty sure the cracking is actually the spark going to ground through the coil pack body, for this to happen there'd have to be really high resistance somewhere in the wires or plugs, or your wire routing is not right. To begin with I'd ohm the plug wires and make sure none of them are open, resistance will be in thousands of ohms but probably shouldn't be higher than 5K or so given the length of the wires. I have Bosch wires and they were all at 2500 or so when new.
Did this happen once and then you replaced the wires and plugs and it keeps happening to brand new coil packs?
EDIT: One other thing to check is all the wiring going to the coil pack, these wires are known to break and cause problems, so give that a good visual inspection.
Last edited by 6SPD_soul; 11-16-2012 at 10:46 AM.