Strange low frequency noise

Somebody close to you running a pump or dehumidifier?

Could be tinnitus from covid.

Do you hear it in both ears or only one?

Lie down on your side with one ear flat to pillow.

Does the location of the sound seem to.l shift?

Put ear plug in the other ear and repeat.

Might help you to figure out if hearing it internally or externally.

A Heat Pump somewhere ?

It could be that covid has made you more sensitive to certain frequencies? Ever since my bout back in 2021 I have been far more sensitive to low frequency noise, be it from diesel engines, construction, pumps, water moving through pipes, refrigerator's, oil boilers, electric cars charging etc. Low frequency noise is everywhere, all the time, most people just don't notice it or can filter it out.

Unfortunately low frequency noise can carry for many kilometres, easily pass through solid walls and even resonate in buildings. If earplugs work for you then use them. I see you've already tried turning off the power to no avail, so the noise is probably external.

Only the LNB on a satellite dish isn't passive, and they don't emit noise. An EV charger might

its probabaly Millhouse.

I have the exact same thing, I was convinced it was an electrical hum from my house somewhere. It drove me crazy trying to find it. I then noticed that I also heard it at two other houses which I spent the night at. I tend to hear it only at night, or during the day if it is v quiet in the house. It tends to be the same ear, so I am thinking it's all in my head. I never hear it when outside, at the office, etc.

My initial thoughts were that this sounds like mains hum, i.e. a 50Hz audio signal derived from the the 50Hz mains electrical network. However, you've measured 47Hz with a phone app which is well outside the mains frequency's allowable range 50 +/- 0.5Hz (long term average tolerance is much smaller).

I'm not familiar with the app you're using but it's worth confirming if it's misreading 50Hz as 47Hz by changing the settings for max resolution. If you still get 47Hz then one final check would be to generate a 50Hz audio signal with a phone or PC app and see if you measure it as 50Hz or 47Hz. If it's the former then you really have a 47Hz tone and if it's the latter then it's probably 50Hz mains hum.

If it's 47Hz then I'm not sure what could be causing that. It's unlikely to be a pure beat frequency (50Hz-3Hz or 97Hz-50Hz), so more likely some mechanically derived audio signal, perhaps the wind acting on the satellite dish etc.
If it's 50Hz then you need to turn off all power at the ESB consumer board ("fuseboard") isolation switch, which I think you've done but to no avail. The next thing is to check if you still hear the hum when power goes off in the neighbourhood. If you're like me then you'll have a planned/unplanned neighbourhood power outage once or twice a year, just make sure you check if the hum disappears or diminishes in all locations and if it returns to normal the minute power is restored.

If the hum is from the external (to house) electrical network, you could talk to the ESB or you could ask your nearest neighbours to turn off their power at the mains isolation switch and work with them if the problem comes from their houses.

Would it be mmm-mmmmm or would it be mmmm-mm? The first one there, now that’s the sound of a fridge humming and the second one, now that’s the sound of a man humming. You never hear a woman humming. I knew a woman once, but she died soon afterwards.

I have heard this as well. Like a previous poster I thought it was from the fridge or something else electrical from within the house but after turning everything off I could still hear it. I then realised I could hear it outside the house but couldn't find what direction it was coming from. Have also heard it in a neighbours house.

There was a programme on BBC a few weeks back about a lot of residents in Omagh hearing an unidentified hum sound.

Article here about possibly identifying the cause:

https://bbc.com/news/articles/cmm3jerqvero

Coil whine ? Nothing worse if you are susceptible to hearing it.

Any of the crash test dummies living near you???

Yes

Must be Joe Duffy humming away to himself

Would it be mmm-mmmmm or would it be mmmm-mm?

The first one there, now thats the sound of a fridge humming and the second one - now thats the sound of a man humming.

The amount of personal info they ask for! 😯 👀

OP should go full on Chuck McGill ripping the house apart to get to them bottom of it.