high frequency intermittent noise

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


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.
The power cord is my antenna, I switched to a non-audiophile power cord and was able to move the power cord around, up, down, and around (could never do that with what I am using), and yes, I could affect the noise.

I'm wondering if I'm now in the market for a new power cord?
almarg7,616 posts11-16-2017 3:32pm
Good point by Ralph (Atmasphere) re the possibility that the amp doesn't provide grid stopper resistors in its design. If that proves to be the case, James, I would think that if you explained the situation to Vladimir he could have them installed at modest cost. It would just involve the addition of a physically small low power resistor in series with the grid of each tube.

Good luck. Best regards,
-- Al

Agree, but how about when james1969 used the pro-audio monitors for the test. When he hooked them up he heard the same RFI noise. Just a guess the amps are SS.

I just got off the phone with Rob at Furman. He’s a great guy, been in the pro-audio business for 24 years, 16 at Furman. He says he’s seen music studio’s go through the same issue, all of a sudden an antenna gets put up and there’s nothing to do except move. I cannot move, so then he said the next approach is to build a faraday cage and opt for better shielded cables.

This is an air borne issue, the cell tower is coupled to the air, Rob was amazed. I sent him the 2 sound samples I posted here so he could hear.