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.
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

@almarg Terrific find. That would explain why some days it’s quiet, and other days it’s busy. Early mornings 4am to about 11am it’s quiet most days. And it goes on late into the evenings. Yesterday it was very busy all day long.

I also used the Hf35c Rf Analyzer to walk around my apartment with all the power turned off, to find quiet zones, unfortunately I do not have much flexibility in my room arrangement for the system. It’s called living in a shoebox.

I’m not too bad off, the noise is a low level noise, just-at-the-natural-noise-floor of the room. Its traffic outside, people, cars, bikes, skateboarders, road construction, building construction, air planes above, I hear quite a bit.

I have a police station down the street, and a fire station a block down, so I hear a lot of sirens, which may also contribute to the public safety band Al had mentioned above. So between the subway, the cops, and the firemen, my stereo should keep me in the loop.

james1969 OP
296 posts                                                                          11-17-2017 3:58pm

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.
@james1969 ,

By chance does the Analyzer have the ability to indicate signal strength as well? If so walk around your apartment and see where the signal is the strongest.

Next go out the entrance door of your apartment to the central House hallway, corridor, of the floor you are on. Walk the hall in both directions and check for a hot spot in signal strength. Point the device at both walls on each side as well as the ceiling as you walk down the hallway.


The signal strength is an audible on the Analyzer, not a visual indicator, the speaker emits the raw signal noise.  I walked around on my floor and the Analyzer was pretty quiet.  I circled the entire floor...nothing.