high frequency intermittent noise

@almarg I checked 540kHz and for a moment, I thought I was in that movie Contact, I did not hear the noise.  Just static.  Great idea.

@falconquest Thank you for the pointer, I will check that out.

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.

@james1969 ,

The noise is primarily during the day and goes into the evenings, weekends too, early mornings it does not appear.

"early mornings it does not appear." Never? Have you checked the time in the morning the noise stops and the length of time the noise is not present? Is there a consistent pattern early every morning. The noise stops at __ am and starts up again at __ am
Same times every day?

I have a cell phone tower directly across the street from my building in Manhattan.

But the sound is not 24/7.

I live in a pre-war mid-rise building.

How many stories high?

Is there a building maintenance person on duty, someone you could speak to about the noise? If so before you talk to them see if you can pin down the time in the early morning the noise stops and the time it starts back up again.