high frequency intermittent noise

Make sure you look at a Furman with LiFT and SMP.

The SMP surge protection is, by design, a low pass filter. Unlike most other AC filters it works in the audible band, but not sure how low.

LiFT is active filtration. The one thing about Furman, they seem to have 100 different models, so be careful that the exact model you look at or test includes both.

Not sure about common mode noise, but most linear power transformers filter that out anyway.

James, one other thing to try, use an extension cord if you must, but maybe you have other AC lines which are less noisy, or perhaps a place in your apartment where the noise pickup is less?

Just throwing out ideas that are cheap. :)

But yeah, I like Furman for noise and value (especially if you can find them on sale!)

@erik_squires The Furman looks promising.  The P 2400 IT looks like the way to go.

@jea48 The noise does present itself 24 hours a day randomly, it is only the early mornings ~ 4am to 11am it is not very frequent, but it does appear.  The building is 15 stories high.  I have already had 2 different electricians in, and they did not do anything.