Do you have a laptop? Might be a bit overkill, but try running a laptop from battery with the Focusrite powered off it, and shut off the power to the whole house from the mains. If you're still getting the high-frequency noise coming in, then it's something environmental to the area you live in, and if it goes away then it's something powered by your house and you can hunt it down by turning on breakers one by one until you find the culprit. Once you've found the circuit it's on you can experiment with any noise filters or the like that others have mentioned.

I'd suggest using a receptacle tester on EVERY outlet in the house, not just for the noise issues but for safety. Some older equipment (old guitar amps in particular) connect the neutral line to the chassis, where if the live/neutral wiring gets swapped it'd be connecting the live 230v to the chassis!


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