For some time I have battled background noise from a variety of sources within the home office, from the DSL router / modem, to the TV which is about 6 feet away from the TV (usually off) and and other "twitchy" RFI generators in my hovel which other family members use. I have used a variety ferrite cores, etc. with little or no success. The noise floor here averages S5 to sometimes S7. Believe me when I say it's been difficult to catch some of the fainter OP's. Seasoned vets have their own method for dealing with this, and your ideas and stories are welcomed.
But I'll get to the point.
When I was at the local Salvation Army tonight (cheap bastard that I am) I ran into a used 8 outlet Triplitte Internet Security UPS, battery backup, NOISE (I emphasize that word) Protection, and Surge Protection. I paid the 8 bucks (cheap bastard that I am) and brought it home.
I pugged all of the radios, DSL modem, computer....and
WOW! the noise floor that was on the average of S5-S7 dropped to an S3-S4 It was no fluke,...the signal indicator hadn't been that low since I got rid of my my platform shoes in the 70's. Unbelievable...
There are a few of the Tripplites on eBay at varying prices. It's not a "One Size Fits All" Cure-All / Be-All, but it did help here. I wanted to pass this along to those that may be cursed with the AC noise syndrome that made listening a bit difficult at my QTH. Maybe it can help at yours...