I understand it, and I think it's retarded. Occasionally, the back plates of the pickups vibrate and create a ringing feedback that comes through the signal. I just save the foam that comes with EMGs, Duncan, etc. Stuff foam between your pickup and the body, and kill the ringing from the backing plate of the pickup. Why pay for something when you can solve it with crap you might have laying around?
Or just buy better pickups.