The hyper212 is a 140w budget cooler. That means it'll handle @140w worth of cpu heat output at maximum. The i7-7700k is a 100w cpu. At 4c/4t under nominal loads. Once you enable HT, and start loading down 8threads, that'll change. Vcore having much to do with the heat output, some cpus run very high stock voltages, as high as 1.4v, which is the cpus limit according to Intel specs. In bios there's no control whatsoever other than bios own settings, which will enable HT and run all 8 threads under load, so you can expect not only higher temps than normal OS operating temps, but 0 ability to change much, if anything. Bios temps themselves are only important if going above and beyond any reasonable output, if you are seeing temps in the 90's for instance, then yes there's an issue, but anything under @70°C is absolutely normal. The cpu fan will respond according to bios settings and it's curve settings until the OS loads and changes that, so high fan speeds are normal too.
So you have the highest performance, hottest running, Intel lga1151 cpu and slapped a budget cooler on it that's barely over design specs for nominal usage. Add in the fact that windows responds to almost instant changes in cpu heat but physically takes longer due to mechanical process, and you get a fan that constantly ramps up and down.
To adjust fan curves is recommended, but they need to be set sharp, can't be a gradual curve, and mobo software or SpeedFan is best suited for this, bios only changes end points not the middle. You'll need to set the curve to remain below 1000 rpm under @60°C and a sharp climb to 100%duty cycle at @70°C. Normal windows usage will bounce the temps from @32°C to @55°C just opening an app or game, so setting the fan curve over that limit stops the ramping until necessary heat limits go beyond, such as in heavy gaming.
Too many ppl place too much significance on temps below 70°C, when honestly there's exactly none. A cpu at 45°C is exactly the same as a cpu at 65°C. As long as working temps are maintained under @70°C, you are golden. So running the fan slower and a temp of 55°C gaming isn't an excuse to ramp up the fan to get another 5° cooler cpu. It simply doesn't matter.
And yes, the stock fan on most coolers is pretty miserable, vendors are constrained by usage of existing company products. CoolerMaster doesn't make a superior fan, so the hyper212 is stuck with the best CM has. Coolers made by Phanteks, Noctua, Cryorig etc having a serious advantage there.