3W ignitions are grounded through the cap and shield..If the cap is on the plug the ground is good....Ignitions usually don't make any noise, unless the spark is going somewhere it shouldn't.....Mine makes a high frequency noise from the toroid coil, but you have to be really close to hear it..the 3w ignition is inside a box and is potted, so any noise would be muffled...
Some of the early 3w caps had leaky inslulation, so the spark got detoured inside the cap...Could be....