when I was at the back fence. The neighbor behind the yard I mow has a big Labrador type dog that would always bark at me but would never get closer than about 4 feet from the fence. The neighbors yard didn't have a fence and I never noticed the dog out of the yard. I have not seen the dog the last three weeks and I noticed I don't have static anymore on my Peltors when I am mowing near the back fence. I think the neighbors must have a underground electric dog fence and it was causing interference with the peltors. The noise was always a pulsating low level noise. Dog is gone so electric dog fence not on I assume and my Peltors work okay now near the fence.