high frequency intermittent noise


I have a noise issue that is intermittent.  Here is what the noise sounds like:

https://clyp.it/4b233bmm

Here is what I know so far:
  • The sound affects all components and is compounded if all components are turned on.  I have turned off my preamp, phono preamp, leaving just my mono blocks on, and the noise still appears.
  • I have turned off everything and unplugged everything in the house including my dimmer switch, and the noise still appears.
  • I have a pair of pro-audio monitors, self powered with class AB amps, and when I plug those into the same outlet, I hear the same noise coming through the pro-audio monitor.  So this rules out my big system.
  • The noise is primarily during the day and goes into the evenings, weekends too, early mornings it does not appear.
  • I live in a pre-war mid-rise building.  I have no ground, I'm using a Nordost QKore grounding system.  This did reduce the noise floor quite a bit, but has no affect on this intermittent noise.
  • I have a cell phone tower directly across the street from my building in Manhattan.
  • Looking at a real time analyzer, I see peak at 2kHz when the noise appears.
128x128Ag insider logo xs@2xjames1969
Using tin foil (thanks @jea48 ) I was able to reduce the level of the constant noise that was out of balance - the right channel was measuring at about 58-60db and the left channel was measuring at about 53-55db.  This was done using a Radio Shack Sound Level Meter pointing it right up at the Fostex super tweeter.  I was measuring in the early hours (no traffic, all is quiet).  My normal room noise floor during the day is 60+db.  So the noise the system is putting out usually competes with outside noise of my environment.

I lined my right rack (I have two racks next to each other) with aluminum foil along the left and right sides, what little I could in the rear, and I also lined the rear wall behind my right rack.

Now my left and right channels are producing the constant hash (the carrier signal) noise at even levels.  This is a step forward, as before with out the aluminum foil, my right channel was emitting the noise up 5db from the left channel.  Very unpleasant to hear something artificial that is out of balance.  Now they produce the noise at an even level, so I've altered the cellular signal where my right amplifier sits (in the right rack).

Using the Analyzer, I was walking around my apartment trying to visualize what a cellular signal would look like - all I could think was it must look something like a solar flare - magnetic in nature?  So that would explain why I would walk around and hear various levels of signal strength.

So it appears the aluminum foil has altered the cellular band of signal around my right rack with my right mono block.  Now both channels are closer in output level of the noise.  We shall see/listen/hear as the day/week progresses.
I’ve added a photo of my racks so you can see what I’ve done. Basically I’ve lined the racks with aluminum foil, then draped an aluminum foil tent over the power distribution center where all the power cords group together. Time will tell...
Consider snap-on ferrite beads. Relatively cheap. Worth at least experimenting on interconnects and power cords.

http://amzn.to/2hLhLG9

Best,

E