Yep noticed the same thing and also it will ramp up to 100% and then slowly come down after waking the pc from sleep, since the fan control is so poor on the pch i have replaced the thermal interface under the heatsink and set the fan to 8%. The pch/chipset never goes above 45-50c however I honestly wish the x299 dark had a normal heatsink on the chipset and no shrouds on the ssds like the z390 dark.
 
 

i have no plastic covers on one of my x299 darks, simply because i have 2 ek m2 ssd heatsinks that do not fit underneath the covers and i haven't had time to machine them down. Using the fan and thermal pads included the temp of the controller still spikes up and down far more than it does with a heatsink, clearly they recognized the plastic chipset and ssd covers were a hindrance as they removed them from the z390 dark and even at 100% fan speed after making 2 90degree bends and passing over the m2 ssds and then out the tiny rear i/o cover the fan is not really doing anything to cool the rear vrm heatsink so the whole thing is flawed, shame because underneath the covers the dark is gorgeous to look at.