I've found multiple questions that are similar to mine, but not quite the same.
I have multiple LED lights that occasionally flicker (maybe a few times an hour, for about 15 seconds). Not like a "trying to turn on and then turning off" kind of flicker, like a very visible 10Hz-ish-I'm-going-to-have-a-seizure kind of flicker. This happens to multiple lights: bathrooms, hallways on different sides of the house, dining room, and entryway. All told it's three different circuits. When the flicker happens, they all flicker. They otherwise work perfectly fine.
I cannot seem to connect the flickering to anything consistent: sometimes the heater is running, sometimes it's not. Sometimes the fridge is running, sometimes it's not. I tried replacing the light switches on a whim, but that changed nothing. These are all just dumb switches, by the way-- no dimmers or anything.
I don't really know what to investigate, here. My appliances appear to work without issue. My outlets appear to work without issue. I don't notice any flickering in the LED trim lights I put into my pot lights; it's possible those are too high on the vaulting ceiling for me to really notice, but that seems like a dumb explanation for why they don't seem to be flickering when honestly at least half the house seems to be. If I want to go to a rave, I'd like to do so by my own free will.
Update 1: every single one of these bulbs are new, from Home Depot. I recently purchased this house and went on a color temperature matching spree (we've all been there, right?). I just noticed that one of the bulbs in question, in a bathroom, is dead. That seems relevant.
Update 2: Scratch the previous update, that bulb was just loose. Between all of the flickering lights, the brand is the same. The entryway and dining lights use EcoSmart B11s, and the hallways and bathrooms use EcoSmart A19s.
Update 3: I had the power company come out to put a monitor on the system, and they discovered that my junction box was completely full of gopher dirt. Much of the rails had corroded away. They replaced that, thinking it would solve the problem, but it hasn't. I'll call them again.