[Skybird]

Yes, this is also often considered to be a cause, but it is unproven in most cases that were examined, it seems. The interference caused by house walls is noticed by some, while others deny it. Means: some people report they notice a variation in volume depending on how close to a wall they are, or how far upstairs, while others say changing their position in the house or room changes nothing in volume. Higher floors in a house seem to be more prone to "fetch" up the hum.

When I hear it, the volujme does not chnage no matter where in the room or house I am (this is three floors plus roof area and underground basement, five levels all in all) - it also is exactly the same sound volume when I leave the house and even go kilometers away. Only the ammount by which of the hum gets washed out by other environmetal sounds varies. Thats why it is the loudest at night, when everything else is silent. I think it has not changed volume then, only appears to be louder due to other noise not being present.

In general, note that the available material on the hum is limited, and inconsistent. It gets almost no academical interest.