This is super weird

I will not say the following account is paranormal because it sounds too much like someone on a walky-talky or ham radio. It all started last week. I had a gentleman come to the door wanting to buy an old van of mine that sits in the back of our driveway. As I was explaing to him that I wasn't ready to sell yet, we both heard a short blast of a voice that seemingly came from the front staircase or hallway. As no one was even near I wondered what its source could be. The fellow I was conversiong with asked if I had a radio on? I said "No", but I would think a radio would continue playing; not just give a short blast that couldn't be understood. The fellow left and I walked the hallway looking and listening but nothing happened. Later in the week as I was working in the Parlour the "voice" was heard again and a few minutes later even again. There are no radios , walkie-talkies, or two way radios anywhere in the hallway or Parlor, nor outside between my house and the storage building next door. I was perplexed but figured it had to have a logical explaination. The voice , definitely male, is loud but you cannot makle out what is being said. So last night as I entered the masterbedroom with our two schnauzers the voice boomed forth again. Both dogs ran to the wall on the western side of the bedroom and started barking. This wall has a semicircular bulge in it where a dumbwaiter was once housed (It was closed off in the 1950's sometime). I opened the bedroom door to the upstairs hallway by the front stairs and the voice was very loud. It sounded like it was saying, "....AB here..." or something to that effect. I really started investigating the hallway at this point and the voice sounded several more times and I traced it down to approximately where that old dumbwaiter was. There is no opening to the dumbwaiter from the attic or basement or at any point on any floor. It was completely sealed off. What the heck is causing these short "radio?" messages to come booming forth from this wall? I heard this voice at least 7 times last night and the dogs immediately reacted to it each time. Ghost ? I really don't think so; but what on earth is causing it to come through a very old, sealed off, dumbwaiter shaft?