One other thing that comes to mind is the spark plug cap. If it's the type of plug that has a screw on cap, make sure it's tight using pliers. If your ignition has a rubber molded cap on the end of the plug wire with the metal "loop" inside for snapping onto the plug cap, you can try squeezing it (very slightly) with pliers to make sure it fits the plug cap as snug as possible. If it's loose, it can cause lots of stray RF. If your spark plug connector is of the hard plastic or metal variety, then at least inspect it and try to determine if it fits the plug cap tightly.

If after trying all the good suggestions in this thread, you still can't solve the problem, it could be that your iginition module may be faulty. It would be worth sending it in to be checked out and serviced rather than trying to fly the plane with it.