packersfan036 :
asus z170-a motherboard, arctic liquid freezer 240 water cooler, 16gb of corsair vengeance ddr4 ram, msi gtx 970 video card, i7 6700k cpu
Your motherboard has good quality VRMs, you have a good AiO cooler (cooling shouldn't be an issue here), and have supplied enough RAM that the CPU won't have to be constantly accessing the pagefile.
This means that hardware issues are not the cause of your fluctuations.
Likely, it fluctuates because the load is changing. Even when your screen isn't doing anything but sitting at the desktop, Windows is still doing stuff like checking for updates, making sure there aren't viruses, checking to see if you've used the mouse/keyboard, etc.
Your computer is always doing something. This means that CPU load varies from one second to another. It's normal for temps to vary by up to 5C under idle situations and it's also normal for different cores to have slightly different temperatures. It doesn't matter whether you use an AiO liquid cooler, custom loop, or any quality air cooler, temperatures are still going to fluctuate because that is the nature of electronics when they're under varying loads.