Grab a small portable AM radio and walk around your property and the immediate neighbors. I’ve found interference inside my compound using a portable. Many times that same interference will show up on the AM band, with the closer you get to the source, the louder the interference. Dimmers switches and certain Chinese LED lights are many times the culprit of interference. And Plasma TVs give off enough RF to give one a sunburn. Those things are just nasty.
That's exactly how I know it's in their house.
Related story: I used an old shower radio with the AM band in it to find a break in my dog's electric fence. Handy things, those old AM radios!
I live approximately a half mile from a Walmart and when plasma TVs came out there was so much RFI you could fry an egg. By the way, the Santa net is up every night on 3.916 MHz starting at 7:30 pm central.