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.
kosst amojan said:
Might mu metal be more effective than aluminum foil?
@kosst amojan

Probably, not sure. I just figured he could pick up the aluminum foil locally.

By the way I think you are right in thinking the cell tower is not directly the cause of the noise. It may be indirectly caused by the cell tower because of cell phone equipment installed on the floors of his building though. There may be one on his floor. In the corridor or a housekeeping closet or a small mechanical/electrical closet. A suspended acoustical tile ceiling is a great place to hide the small antenna.
The old prewar apartment building could have thick outside walls made of concrete and brick. Hard to say. James1969 could see how thick by just looking out the side of the window for how thick the outside wall of the building is. Floors can be thick concrete as well. It depends on the type of construction and building materials that were used.

Yes, concrete and brick, 14" thick barrier wall. I’m in a concrete box basically with brick on the outside.

I did not ground the aluminum foil the first try.  I will try again.
Playing with the Hf35c Rf Analyzer I pointed it to the cell towers across the street, and the noises it makes is higher up in in the frequency range of 1600 - 1900MHz.  Where as the frequency my stereo is picking up is in the 700 - 800MHz range.  So I guess it's not the cell tower.
unless... the cell tower is somehow causing the lower freq. noise - maybe drawing on a power supply or something
... the frequency my stereo is picking up is in the 700 - 800MHz range.
James, check out this link:


The band extending from 698 to 806 MHz is used by public safety services, with part of it also apparently being used in some locations for cellphone or other mobile device communications.

Hope that helps. Regards,
-- Al