Yup, this is possible. My father is a ham (radio amateur) and experienced a lot of weird stuff with RF.
From what I know or learned so far (incomplete)..
a) Modern devices do care little about RFI; they're produced cheaply and thus do have little to no shielding
b) CRTs are sensitive to magnetic fields; their flyback units are akin to strong electro magnets
c) Noise can crawl along the cables; socalled "coat waves" (or mantle wave)
d) Ferrites (ferrite clips) can block coat waves (install them at the ends of the cables)
e) The protective ground on power outlets is not always clean, sometimes it causes radio noise to travel in
f) Some external, higher quality power outlets do have built-in AC filters (caps, coils etc)
Anyway, these are just my two cents. Just read an old article about Atari ST vs C64 in the shack.
Turned out the C64 had a bad shielding; the keyboard was the culprit of noise. Some hams used the shielding of their RG58 cables to fix the C64.
They removed the shielding net/grid safely from the cable and imposed it over the keyboard cable (and grounded the shelding.)
Btw, something similar was mentioned in the book "Radio&Computer" by Mr. Gongolsky.
At the time (1990s). he wrote that cheap PC keyboards do have noisy keyboard controllers inside. No shielding, at all!
Edit: Added some pictures of the ferrites that I meant.
One is built into a good USB cable (orig. printer cable), the other one was attached manually to a cable modem's PSU cable.
From what I read in a HAM magazine, some people reported that noise went down by 36db after applying such a ferrite to the PSU cable of a DSL router.
Not sure if the numbers are right, but attaching such a little ferrite shouldn't hurt (please prove me if I'm wrong).
Edit: The microwave problem is special, though, I believe.
Such a beast draws about a kilowatt, which can cause extreme fluctuations in the mains. That's not very friendly to a PCs swichting PSU, either.
There must be a reason why some step-down / step-up converters are especially labeled "PC compatible".
I assume these PC PSUs (and the monitor) were constructed with a more or less clean sine wave on the AC in mind.
So the mircrowave oven is essentially the worst case scenario here, being a giant RF generator.
On the other hand, both devices were meant for home or office use, so there must be a way to solve this conflict.
I'd check if it is possible to install some filters between the power outlet and the PC.
Or I'd check if the PC's or microwave's AC plug is correctly installed in the outlet (phase on wrong pin ? / hot vs cold)
Here are some links, that I found while searching:
https://www.quora.com/Why-doesnt-it-matter-wh … he-power-outlet
https://www.thespruce.com/checking-for-incorr … -wiring-1152518
The Seven Types of Power Problems
https://www.apc.com/salestools/VAVR-5WKLPK/VA … WKLPK_R1_EN.pdf
That being said, please be careful with the mains. Don't do any tests/experiments when you're alone.
Some households around the world still have no residual-current circuit breaker as standard, also.
"Time, it seems, doesn't flow. For some it's fast, for some it's slow.
In what to one race is no time at all, another race can rise and fall..." - The Minstrel
//My video channel//