[RFI] Weather related RFI

[Gary Tuck]

Last winter I had almost steady RFI most every day, most hours of the day.  It seemed to begin when new neighbors moved in next door.  As the weather warmed in the spring, the RFI disappeared.  Then the neighbors moved and I had hope they took the noise source with them.  They are gone but the weather cooled yesterday and the noise is back.  The house is vacant.   So, now I have to get serious.  The only sources I've had in the past are power line noise and defective lights.  I've tried turning off every circuit in the house last winter and I'm convinced it isn't within our home.  It's steady, raspy but not sputtering. I was assuming that it is a portable heater of some kind but what common sources are there related to cold weather?  What might I be looking for?  
Thank you!