I have a similar issue, only about 4:30 AM ET. I am not always up at that time, but when I am I experience the exact same thing.
I believe it's probably something like they are rebooting a server of some kind. It's probably servers local to our regions. I am in New England.
It's highly annoying. Sometimes it happens late at night as well but that is erratic. 4:30 AM seems to be routine.