The likely suspects in your noisy area are fluorescent lamps, electrical motors, and CRT monitors or TVs.
Start by turning off these items, if present, one at a time, to see if you can pinpoint the source of the noise.
If none of those types of things are in the room in question, examine to see if anything of the sort is plugged into the same electrical circuit you are using for the amp- IOW, look for things elsewhere in the house that are connected to the same circuit.
Sometimes, though maybe not very popular in this crazy-heat summer, the better/faster way to find the culprit is to open the circuit breaker box and turn off all the circuits, except the one that's powering your amp (and any effects boxes). That way, you know beyond the shadow of a doubt that you can indeed achieve a hum-free sound in your home. If it's still gonzo noisy, then make sure everything else on the circuit is turned off, leaving your amp as the only "consumer of wattage" in your home. Conversely, you can move to another circuit (probably a different room, perhaps even on a different floor). being sure to turn off the first circuit at the breaker box. Again, make sure the amp is the only thing turned on in the entire house.
If, after all that, it's still noisy, then you have one of two problems. The first possibility is that you're getting very dirty power from the power company. Sadly, that's not usually something you can "prove" to them, so it can be hard to rectify this one. The other possibility is that you're in a so-called "industrial zone" - somebody nearby, with lots of machinery, is generating huge amounts of electromagnetic interference. This is also in the "that's never gonna get fixed" category.
Most weeks, I play in a bar that's in the latter zone. My QtB shielded Strat has no issues whatsoever, it's as quiet as the best hummers I've seen/heard. Some of the "cheaper" rigs are nasty to the point of being outright unusable, sad to say.
Rule #1: All Lives Are Final. Make sure that the life you have just been issued is appropriate for your needs, before departing the womb.
Rule #2: In case you don't like the life you have, see Rule #1.