I am glad you have decided to diagnose the problem rather than throw parts at it as we so often see here. Why not disconnect your knock sensor and test drive without it to see what effect this my have. It may help you learn more about the characteristics of the problem and if whether it really is ping.

My experience with wires has always been that you would get missing, can't really see how they could advance the spark.

Another thought. You say it only happens under a certain load conditions. Not sure what speed/rpm conditions you need to reproduce the noise but what about this. Park car with E brake on full, leave car in gear (I assume automatic) then get under the hood, carefully listen and explore while CAREFULLY advancing the throttle to create the load you need. Better still put the front bumper on a post or concrete wall. You could also have a reliable trusted assistant advance throttle while keeping foot firmly on the brake.
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David Hunter