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.
128x128james1969
That is GSM noise-your (or someone nearby) cellphone is being "polled" or is polling the basestation nearby....earthing(use copper pipe in bathroom or kitchen) may well fix...if not then chokes on power cables is another avenue to explore...and of course keep mobiles charger off hifi circuit.
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I found a set of RCA shorting plugs. I turned everything off except for one mono block, inserted the RCA shorting plug, and the noise is still present.

I tried a different power cord, and the noise is still present.

I tried an XLR cable between my power amp and preamp, the noise is still present.

I have ferrite beads (made of material 61) on order.
Sweet lord, you poor man.

So.. Those copper mesh curtains.. You could lay one on the floor, stack your equipment on top, then wrap the curtain up and over, creating a true faraday cage, as long as you remember to ground it to a pipe or the ground in your outlet. Test to see if an actual faraday cage works.. If so, you could build a nicer looking one integrated into your rack.
I found a set of RCA shorting plugs. I turned everything off except for one mono block, inserted the RCA shorting plug, and the noise is still present.

Try this.
Do you have a roll of metallic tin foil in the kitchen?

Unplug all the other power cords from the AC power outlet. Reason? To eliminate the chance they will/are acting as receiving antennas and induce the RFI signal into the power cord of the mono amp.

Wrap the tin foil around the speaker cable for the one mono amp being used for the test. Be careful to keep the tin foil back from the amp terminals as well as speaker terminals. An inch or two is fine. (metallic tin foil is conductive). For the test the foil should not need to be grounded.
Plug the mono amp directly into the power wall outlet. Check for the RFI signal noise.

Still there?

Next thing to try.
Wrap tin foil around the power cord for the mono amp. Just the cord not the plug body or the IEC connector. (remember metallic tin foil is conductive). The tin foil will shield the hot, neutral, and equipment ground wire. The tin foil should not need to grounded for the test. The tin foil should reject the RFI noise, if it is radiated through the air, from entering the conductors of the power cord.

Plug the mono amp directly into the power wall outlet. Check for the RFI noise.

If the noise is still present you might try earth grounding the tin foil. Though I think it would not be needed for the test.
You will need a piece of wire. Any size will do. Bare one end of the wire wrap it around the tin foil, at the plug end of the power cord, a couple times or so and then twist the wire to itself to secure it around the tin foil. Bare the other end of the wire, amount stripped depending on the wire gauge of the wire. You may need to fold it over itself a few times to increase its’ effective size. Insert the wire in the "U" shaped equipment ground hole of the wall receptacle.