Constant low level hum in flat - any ideas what this might be?

[PunishmentRoundupWithJoon]

There's a constant low level hum in my flat and it's driving me quietly crazy. It's been going on for as long as I can remember. At least two years, possibly four, I honestly can't say. The only thing I know for sure is that it hasn't been present the entire time I've been in this flat (18 years).

Its not my fridge, the boiler, or anything else in my flat. It can't be extractor fans as the bathrooms and kitchens don't have them (I know....great, right?)

Due to the structure of these flats (a high rise), it's often very difficult to establish where a noise is emanating from - you may think it's coming from the flat above but it turns out to be four floors up - or in the lobby!

Lying on the kitchen floor with my ear flat against it (as elegant and dignified as you might imagine), the hum increases significantly. This leads me to believe it's coming from the flat directly below me but again, because of the flats construction, it could just be being transmitted through the floor. Perhaps I'd get the same effect with my ear flat against the ceiling but that's going to be awkward...

I'm finally going to pursue this with the housing association. Before I do though, it'd be really helpful to get any input from anyone else who has experienced anything like this. Do you have any suggestions as to what this may be? Has the same thing happened to you and did you eventually locate the source?

Sorry it's long, am now desperate....

Some kind of air conditioning from the flat below? Or a computer / console fan?

I did wonder about air conditioning. Don't think it could be the console fan as it's constant - apart from a few seconds here and there where it stops (that's what convinces me I'm not imagining it!) and then starts up again. And don't think I'd be able to 'feel' it as I do.

Electricity circuit board?

We live in a terrace and for a long while could hear the extractor fan from the bathroom in the flat next door. That wasn't constant but we knew whenever they were using the loo - bit disconcerting. They fixed it in the end.

Bees or wasps nest in the outer wall?

Or weed farm below maybe

@squeaver - yes, I'd think extractor fan too if our flats had them. The housing association says it can't install them as the bathrooms have no access to the outside. All we have in the bathroom are vents.

@Valhalla17 - have thought about this!! Its perfectly plausible, given some of the people in this block.... Would their 'equipment' cause a constant low frequency rumble??

Weed farm is possible as the equipment does make a humming noise I think, but I expect you might smell something too?

@Valhalla17 - there's frequently a smell of weed but that's because (I've always presumed) the neighbour opposite smokes a fair bit of the stuff. Maybe it's seeping in through the floor or vents??

Thing is, from what I can see, I'm sure the downstairs neighbour has no curtains - surely if there's a weed farm they've have those? Mind you, they are 5 floors up so it's not like anyone will be passing...

I have a constant low level hum and it is my neighbours megaflow water tank.

@roses2 - that must be annoying! Is it likely my neighbour would need one of these when we all have boilers?

Google "The Hum"!

@YukoandHiro - yes, I've done that 😁It's definitely not that though as I don't hear it anywhere else! And according to a staff member I spoke to, there've been no other reports. It's just me!