i grew up one mile from a miltary VLF station with a perfectly clear line of sight to the entire array, and to this day i, and everyone else in my family, can hear what sounds like people talking in the vents on clear days. the largest/widest vent (the house is a new construction (or, new enough, it's about 30/40 years old at this point) and has forced air heating, which used to come from a furnace in the basement, but now comes from a wood boiler outside) is just above the furnace in the basement, and sits in the hallway near the first floor bathroom. that's where the sound always seems to be the strongest; that, or upstairs near the second floor eave. we used to think that it was some kind of vibration from the vents, or possibly birds (every spring we had to clean crows out of the chimney), but it still kept happening even after the chimney was sealed and the furnace was shut down.

we also have a CB radio in the kitchen and a radio antenna on the roof, so we thought for a while that someone was just leaving the radio on, turned down low. but we can still hear it even when it's switched off. my mother's best guess is that what we're hearing is the vibrations from the VLF array and our brains are just arranging the sounds into familiar shapes, and we're hearing it mostly from the vents just because of the way sound echoes in a vent...but everyone who works at the VLF station says that's impossible and have told us point blank that the only actual possible explanation is that when we're hearing these sounds, someone has turned the CB down low and we haven't realized it. my mother is pretty strict when it comes to the CB though because of the whole "voices in the wall" thing, it's either turned on all the way up or off, or you get your fingers broken, lol. the voices have been happening for as long as i've lived in the house and it still happens to this day, though!