Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.
When I lived in my parent's house I had the same sort of problem. In my case it was noise from the High Tension power line tower in my parent's back yard and it was constant. There was no where in the house that was safe.
In your case since it is intermittent I would recommend moving the monitor to a different wall and see if that solves your problem. Also take notes of what is going on when the wobble starts to happen. Is and appliance on that is drawing power from that line? Did the Heater/AC just kick on? Did the neighbors possibly turn on a TV on the other side of that wall? Hope you fix you problem. The way I had to fix mine was to keep the monitor at a 60Hz refresh rate.
My monitor wobbled when it was close to my friends window fan... Look around for something that's ON, and turn it off. Then see if your monitor's still jumpy.