This is quite strange but for the last couple days there’s been a strange humming/ringing sound emanating from a few of the walls in my apartment. I’ve done a couple tests to try and sort the source, I can’t be sure but I think it’s related to the HVAC. I first noticed it in the living room and in the primary bedroom from the wall that shares with the HVAC closet, but then I noticed it was also very audible in the bathroom which is nowhere near the HVAC closet, though i don't know how HVAC works and maybe there's ducts all through the walls (I want to note that the thermostat is currently off, no AC or heat is on currently, this sound is actually coming from the walls not the vents).
I wondered if it was maybe electrical so I switched off the main breaker and the sound continued, so that leads me to think it’s more likely an HVAC issue, but again i'm not an expert.
I’ve never heard a sound quite like this in the unit in the 2 years i've been here. It’s definitely new, it’s like a very high pitched hum, and it goes on for 20-30 minutes then stops for a while, then starts up again, and for some reason it seems to be either more present, or maybe just louder, in the evenings/at night time.
I tried turning the air back on to see what would happen and it only made it worse, the air sounds very different than usual, again this high pitched ringing underneath the usual sound of the HVAC running which is very weird and abnormal. I cleaned all my vents, it’s definitely not coming from there, and I can actually hear/feel the humming very very clear when I put my ear to the walls in the spots it’s generally emanating from all over my apartment.
I’ve attached a video, its not great since it’s obviously hard to capture something subtle like this, but this is in my bedroom you can hear the ringing that’s coming through the wall pretty clearly if you turn your volume all the way up and put it to your ear.
Before i bring in my landlord, i want to turn to the good people of reddit, maybe this is a simple fix? or maybe you know exactly what's causing this? either way, any input would be appreciated!