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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.
james1969
james1969's avatar
james1969 OP
347 posts
 
As I was writing my last post I realized another important fact:
  • The subway runs under my building.
I just noticed the noise appearing when I listened for a train to go by.  There seems to be a correlation here, perhaps it's the subway system:  when I hear the subway go by, the noise is apparent.  That would also make sense in that the subway does not run as frequent in the early hours of the day.
willemj
1,036 posts
 
I could not quite figure out what happened when yo used a battery powered radio. Does it come through your power lines or through the air?
james1969's avatar
james1969 OP
347 posts
 
@willemj Very good distinction.  I think the battery powered radio was a test to see if it was air born, which leads me to think it is not.  So then it is in the power.  I hope this is the case.  I have a Furman P-2400 IT on order, I'm going to give this a try.  @falconquest and @erik_squires are pointing in this direction, and I have not tried this solution yet.  I will report back my findings on the Furman.
willemj
1,036 posts
 
Those ancient subway trains can probably produce quite a bit of power line pollution, but I would expect that system to be completely separate from the domestic power, given that trains run on much higher voltages. Still, your domestic power system could perhaps pick up some noise. Did you call the electricity company?
james1969's avatar
james1969 OP
347 posts
 
I live in a neighborhood where we have the oldest electrical system in the city.  A few years back, an underground power transformer blew up and caused quite a stir in the neighborhood - black smoke from the electrical fire coming out of a manhole from the street. 🔥 

Nothing gets replaced unless it fails, so it would seem for my neighborhood.  I don't think the electrical company would even give me any time considering the issues they are dealing with. 😊
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