This is 90% of my job every day. Something in your house is acting like an antenna and interfering with the return path. Most of the time it’s a loose connector behind the modem but any bad connection can cause it. I usually track the noise to a house and use a filter at the tap that blocks the noise and leaves the sub online, then create a job to get an tech in the house

I’m a lineman for Comcast, there’s definitely power backup for every node. How long they run depends on the current draw of the system, but they’re usually a couple of hours at least. We get dispatched to hook up generators when the batteries get low