A couple of weeks ago, I noticed something on my Windows 7 PC was using 100% of a core all the time. I finally tracked it down to Windows Update the other day. It can't finish 'checking for updates', either automatically or manually.
So I just turned auto updates off. That PC is really only used for games and video editing anyway, it rarely touches the Internet. I'm guessing they're trying to screw Windows 7 users to try to convince them to downgrade to Windows 10.
But supposedly Microsoft have some tool you can download to reset Windows Update and get it to maybe work for a while again.