Funny, but incorrect. This mostly has to do with spurious RF noise generated by badly engineered devices like power supplies or manual light dimmer switches - things that aren't designed to communicate. Manufacturers are supposed to test for these sorts of emissions, but frequently don't.
Meaning you're claiming in a cities NYC & DC that the NSA doesn't to full spectrum dumps, right? Or that they would have not looked into statistically unusual high amounts of background noise?
If the NSA does this, they'd have the info. If they don't, I'd be curious why; meaning legal, physical limits, etc.
This has nothing to do with the NSA, and the NSA has no interest in RF noise. The noise isn't some encrypted electronic communication. It's electromagnetic noise as a byproduct of poorly designed electronic products. It's like if in a chemistry lecture if all the students started humming, it would become difficult to hear the lecture. So there is no connection to the NSA.