At our old place we had the 'hum' pretty bad. It was very pronounced. I actually found out about the whole phenomenon because of this. I went
searching for why I was hearing 'idling train locomotives' all night long when there were no trains nearby.
Being of a physics background/education I'm not easily taken by 'fantastical' explanations favoring instead more rational ones. I actually did a fair
amount of research and experimentation into what it was. I don't think I ever truly solved what it is, but here were some of my non-scientific
observations and quasi-conclusions:
a. The hum is much more pronounced inside a dwelling than outside the same dwelling.
b. The frequency of the hum (in our case) was determined to be around 80Hz
c. The amplitude of the hum was at or below 0dB
d. Windows and doors being open did affect the hum, but not significantly (i.e. it could still be heard / sensed)
e. Location and type of structure definitely affected the occurrence and prominence of the hum
f. The occurrence of the hum was independent of power being on or off (i.e. it could be heard during power outages)
g. The hum did seem to be more pronounced at very cold and very hot outside temperatures, but could be heard / sensed through all temperature
1. The hum definitely seems related to a structure / dwelling (houses, buildings, etc.)
2. The hum does not appear to emanate from mechanical devices
3. The hum does not appear to emanate from an electrical source (i.e. 60Hz electrical power)
4. The hum does not appear to emanate from a geologic source, because it is more pronounced above ground than below
Ultimately my non-scientific conclusion is that the hum is related to a resonant frequency created within a structure as a result of passive air
movement through the same structure.
One other note; I owned the house for roughly 15 years and over time the hum seemed to get worse (or maybe I just noticed it more). When we moved to
the new place I no longer heard the hum (at all). And, I haven't heard it since.
ETA...Oh, and I did check to see if there was any unusual RF background noise with a spectrum analyzer and found nothing unusual, so I don't believe
it was RF related.
edit on 12/29/2016 by Flyingclaydisk because: (no reason given)