high frequency intermittent noise

@toddverrone

That’s a great find. Let’s say I get ferrite beads in place. I still have tubes out in the open where the audio signal goes through as well. I think there is no escape...

@kosst_amojan- is it possible that the building itself is set up with these devices you identified? (They seem to act like repeaters, to increase strength within buildings). Unless a neighbor set one up to improve his/her cell reception, as @jea48 alluded to, why wouldn't the building itself provide such a facility? Given the density and height of the buildings in Manhattan, I remember encountering dead spots in coverage walking around on the streets (granted, this was some years ago, I haven't done that for quite a while, and now no longer live or work in NY). 

Here is another recording taken early in the morning with no subway cars under my building:

https://clyp.it/ae0xgczb

Note there are 2 noises:

1. The consistent hash/whine
   
2. The intermittent noise
   

This is the worst I've heard it in the mornings.  It only lasted for a minute and a half, enough for me to record the 1 minute clip.

The Furman has buffered me from my refrigerator noise, I would hear a *click* in my system when the refrigerator would turn on, now it's silent.

@whart 

There is now cell phone reception in the subways too.  So each subway car or perhaps the subway tunnels are lined with these devices.

@james1969 - alas, another quiet oasis in NYC gone to hell. 
This thread is fascinating to me for the deductive work- i know suffering the noise sucks--we've probably all had our share of imponderable issues at times- but i'm learning as i read this. 
The solution will probably be something obvious and stupid (e.g., did you plug it in?)
In the meantime, here's my tin foil hat conspiracy theory connect the dots, Elvis is an alien idea: if the subways have these critters, and the noise coincides with the passage of a subway under or near your building....?