The “3D” graph is really just GPU utilization. There are other aspects of the system that will utilize the GPU, like the Desktop Window Manager or Hardware Acceleration in your web browsers.

You’re going to want to make sure the noise is indeed coming from the graphics card. CPU will also fluctuate in load / frequency and most fans’ speed logic is bound to that.

I’ve found that, a lot of the time, this repeated “revving” is the result of something crossing a threshold in the fan curve. Adjusting the fan curve can help avoid that crossing that “cusp” back and forth.