I had a chance to do an interesting experiment, just a little while ago.

The power went out in my house, and I assume the entire street/block, for about 30 minutes.  So, I thought it would be the perfect time to hook up my new backup battery, and make a few contacts.  I had it connected to the K2 in no time (power poles for the win), and was quickly on the air.  The first thing I noticed, was the lack of background noise.  It was dead silent.  I mean S0.  Nothing but clean CW signals coming through. I spun around the band, and made one quick SKCC contact.  

When the power came back on a few minutes later, the background noise jumped up to between S1 and S2.  Not too bad, but it was noticeably louder.  Taking it a step further, I went around the house turning stuff (TV, computer, etc.) but they didn't seem to make much difference.

So there we go.  Definitely some noise around here, but I guess that's the price of living in a metropolitan area, and having your antenna in the attic.

In town noise is S9 on 40 meters and 20 meters.  A few miles out of town noise is S1.

This is why my primary Ham activity is SOTA.

My nose level varies from day to day.  Sometimes it's S1-S2 (on 20m), and other days it's S7-S8.

Plus, I have a "blob" of noise on 20m, every day, that migrates around the band.  It looks like a "mound" on the panadapter, that is maybe 15kHz wide, and  S5-S6 at the peak.  And, it is at a different place on the band every day.    One  day it will be around 14.020.0, and the next day it might be up at 14.055.0.  It can be quite annoying at times.

I live in a pretty rural area (1 house per 2.5 acres is the max zoning density, and not all lots near me have homes)
a few years ago at least a couple neighbors had plasma TVs, I'd see S7-S9 noise routinely.

By far the bigger deal has been power lines. Had a pole with a bad transformer nearby that would
hit S9+20 but go to S0 in a storm. It took a few tries but the power company did eventually get that
issue fixed.

Out at my ranch, there are maybe 10 homes within a mile of me, ironically my closest neighbor
is active on 1.6 MHz. Dead silent except for signals and obvious atmospheric noise.

For the last couple of years I've been crossing my fingers for such a thing to happen in my neighborhood so that I could narrow or eliminate possible noise sources outside of my house.  Of course now that I have radios, battery backup, inverters, and a generator that will probably never happen



I was able to find and eliminate several noise sources in the house (my "food saver" vacuum sealer being an odd one) and get the power company to knock out several power line noise sources (now that was a multi-year ordeal!), and now the noise on the higher bands is at an acceptable level, S3 or so at the most.  40M and lower bands are still damn noisy, S5 or more, but it is more of a white noise than an identifiable source.  Struggles of living in the 'burbs.