Strange talking in the hallway

I still have it. Its loud, its garbled, it still seems to be coming from a section of wall adjacent to the master bedroom. In an area where a dumbwaiter once existed. Its an inside the house wall. I'd swear it sounds like a shortwave radio or walkie-talkie. It doesn't last but a few minutes, sometimes, just a few seconds; but what can be causing it? This voice, seemingly male, has punctuated the silence of the upstairs hall , off and on, for several months now. Its a mystery I cannot find an answer for and its driving me batty. I have no close neighbors on any side. My closest neighbor is across the street from me. The nearest neighbor behind me is a quarter mile away. I have a warehouse where I store things on my left side and a wide lawn and old block, two stall, garage seperates me from my neighbors on the right. My dogs hear the voice and react to it by running to that upstairs wall and barking. This is not to be confused with the downstairs wall next to the library that the younger dog frequently backs at. I have recorded the voice but its no clearer on play back then it was originally. For this event there has to be a logical explaination. Does anyone out there who is knowledgeable about short-wave or walkie talkies have any idea how anything in this old 1857 structure could possibly be picking up such signals? Or do I actually have something paranormal?