Ok I’m in Singapore…power is generally stable but could be polluted with who knows what.
Military who know what they hide out there, there is a camp nearby but have had this sound in one form or another in another location too over 10 years ago…all gear pretty much has been changed.
No pacemakers etc nor TVs on either. AC was off too when everything was off. AC Was on at the time of the recording
I can’t hear it at the speakers…my wife can…I can hear it on the recording…might just be below my threshold at that level.
Recording was in a noisy room so ignore the background noise and was recordered hand held a few cams in front of the tweeter with an iPhone
Seems not to be related to volume settings. Hard to hear when music is playing. Is not present when the system is off, and other things in the room remain on
Doesn’t appear to be present on tv speakers or other small speaker setups like Oppo sonica speakers when idle, or RPi with dac amp hats when music is not playing but these could have auto muting and idle shutdown
I’ll post a system components list at some stage too, but as I have said it’s a problem that has been around over 10 years in 2 different consecutive homes and many different equipment changes.