I usually don’t unplug my speakers (active studio monitors Adam A5X) from the power outlet, but when I do, there is temporarily - usually for a few minutes - a very high pitched whining, almost signal like, noise coming from the tweeters when I reconnect them to the power outlet and turn them on. I don’t know much about electricity, but if I may make a wild guess: could it be the noise/subharmonics of some capacitors being “refilled” after being completely discharged upon being disconnected from the power outlet? But then again, wouldn’t that happen in a few seconds?
I am very eager to learn!
It’s almost always the caps (capacitors). They have a very distinctive whine while energizing, and it can also cause some reverb in the speakers. It settles into a subtle whistle when fully energized. 40 some odd years and I can still hear them every time I turn on a computer tower, a TV, an amp, etc. I’ve learned to tune them out most of the time.
Came here to say this. If it sounds like a disposable camera charging its flash or night vision goggles in a video game, it’s probably some capacitor(s).
Maybe high frequency pickup on the ground/input causing the internal amplifiers to oscillate. It be EMI from its own internal power supplies. If you have something like LED or fluorescent lighting it might pick up high frequency noise from that.
Could also be the ripple on the power supply increasing as the voltage drops from having no input.
Perhaps try using an app like spectroid to try and figure out what frequency the noise is
I’d imagine it’s the electronics before the amplification stage being energised and the resulting noise is being amplified and sent to the speakers. Or it could even be the amplifier itself powering on and letting noise through. I don’t know much about the specifics beyond that, though.
