high frequency intermittent noise

For those who thought the noise is GSM, I did correlate the noise with the Hf35c Rf Analyzer, but the device only correlated the noise, did not show me the frequency.  I think it was a defective unit in that the display did not work properly.

Well...on the positive side, I've eliminated a ground loop, and have reduced the noise floor in the music quite a bit.  The Nordost QKore took care of my ground loop issue, and the Furman P-2400 IT reduced my noise floor.  

Does anyone have any experience with AudioQuest cables? They appear to have an active shield that is battery powered...

Thank you EVERYONE who participated.  I'm a little tired...but I will get some tin foil now...

@whart Are you thinking tin foil as well?

Tin foil had no affect on the power cord.

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.

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.

@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.

@jea48 

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.

Using tin foil (thanks @jea48 ) I was able to reduce the level of the constant noise that was out of balance - the right channel was measuring at about 58-60db and the left channel was measuring at about 53-55db.  This was done using a Radio Shack Sound Level Meter pointing it right up at the Fostex super tweeter.  I was measuring in the early hours (no traffic, all is quiet).  My normal room noise floor during the day is 60+db.  So the noise the system is putting out usually competes with outside noise of my environment.

I lined my right rack (I have two racks next to each other) with aluminum foil along the left and right sides, what little I could in the rear, and I also lined the rear wall behind my right rack.

Now my left and right channels are producing the constant hash (the carrier signal) noise at even levels.  This is a step forward, as before with out the aluminum foil, my right channel was emitting the noise up 5db from the left channel.  Very unpleasant to hear something artificial that is out of balance.  Now they produce the noise at an even level, so I've altered the cellular signal where my right amplifier sits (in the right rack).

Using the Analyzer, I was walking around my apartment trying to visualize what a cellular signal would look like - all I could think was it must look something like a solar flare - magnetic in nature?  So that would explain why I would walk around and hear various levels of signal strength.

So it appears the aluminum foil has altered the cellular band of signal around my right rack with my right mono block.  Now both channels are closer in output level of the noise.  We shall see/listen/hear as the day/week progresses.

Here is some interesting shielding:

https://hollandshielding.com/content/Filemanager/PDF_Catalog%20cable%20shielding%20[English]_November-18-2010-219pm.pdf

@erik_squires 

No problem, I have 30 days to return the Furman.  But I think it's a keeper.  The issue presents itself with only the bare amps turned on.  I was using only 1 amp only for some testing.  Even the powered speakers have this issue.

I’ve added a photo of my racks so you can see what I’ve done. Basically I’ve lined the racks with aluminum foil, then draped an aluminum foil tent over the power distribution center where all the power cords group together. Time will tell...

@willemj Great link, lots of interesting articles there.  Thanks.

@jea48 

I'm with you man.  Check this out:

https://www.select-fabricators.com/rf-emi-shielding/rf-emi-test-shielding/curtains/

I need to get more aluminum foil...

Try adding a choke across the speaker terminals to short out the HF signal.

@shadorne 

What is a choke?  How would you implement this?  I'm not an electronics guy, learning-as-I-go-here.

Ferrites are on order.  I still need more aluminum foil. 👍🏻

Aluminum foil had no affect on the power cord and the speaker cable with the shorting plug in the amp.

@xti16 

Very interesting - parts 1 and 4.  I may try to seek these power cables for audition to see if there is any affect.  Thank you for the link.

@fusian  

I am not using a computer as my source.

I tried the ferrites and they had no affect on the noise.

I got a set of Sony WH-1000XM2 Bluetooth headphones and I can hear the noise very faintly in my headphones in my apartment.  So now this verifies that the noise is air borne and not from my power mains.

Thank you all who participated in this thread. 

Thanks...unfortunately a move is not in my playbook at this time.  The noise is not very noticeable once music is playing.  Only when there is no music playing then it becomes noticeable.  So, it's tolerable for now.

It's all about the music...once the needle drops...I'm very happy.

I was on a quest to solve the noise (which I have lived with for some time) and in the process, I resolved a ground loop issue, and inserted an isolation transformer which really did solve a lot of noise from my power mains.  So the system sound has been elevated, just not 100% dead quiet like I would prefer when sitting right up next to the speaker listening for noise.

Time to move on to the next weak link...👍🏻