high frequency intermittent noise

Tin foil had no affect on the power cord.

Did you get the conductive metallic tin foil type? Actually it is aluminum foil.

Did you also try grounding the foil to the "U" shaped equipment ground contact on the wall receptacle?  (You could also use the center 6/32 trim screw that holds on the cover plate. Just make there is not any way the bared wire could come into contact with the hot blade of the plug plugged into the outlet.)

Last thing I can think of is to try the aluminum foil on the speaker cable.

Hopefully the ferrite beads you ordered will work.

I did check on wireless building automation systems. You might want to check with  building maintenance and see if they are being used in the building. I would also ask if there are cell phone antenna devices installed in the building. That's an old building with thick outside walls made of concrete and brick, I would imagine.

https://www.buildings.com/article-details/articleid/15219/title/how-to-boost-cell-phone-coverage-in-...


http://www.facilitiesnet.com/buildingautomation/article/Pros-and-Cons-of-Wireless-Building-Automatio...




 

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.