What exactly do you mean by "fresh installed Windows 8.1 machine"? I got my Windows 8 computer on 2013_12_31, which used the configuration that came with the computer, initially. Then about 30 days later, I got a boxed copy of Windows 8.1. I did a nuke and pave, and all was well. No popups, etc in either case, because when I setup my computer at the end of 2013/beginning of 2014, I turned off all automatic updates, except for AVAST.
Unless you disable automatic updates (windows and other programs), if available, THERE IS A CHANCE that these requests might be valid. Just like on Windows updates, it will attempt to automatically update your system to 8.1U, unless you disable it.
Most PC manufacturers have preinstalled software that "calls home", to see if all the drivers are up to date, and if not, either automatically downloads the drivers, etc and tries to install them, or at least asks the user if it is AOK.
Best of luck.