How come sometimes my fan speed runs ultra fast on TU?

Sometimes when I run TU, my fan speed goes fast, while any other game I run doesn’t have this issue.

Settings are set to “high” and here are specs in case you are wondering:
i5-6500 3.2GHZ (4 CPU)
8GB RAM
NVIDIA GTX GeForce 1060 6GB
(drivers are up to date)

does this mean I can’t run “High” yet I get 90FPS on average?

The more settings are set to high and ultra, the harder your system is going to work to pump out the frames, which will create more heat, and cause fans to spin up to keep them cool.

Limiting your FPS can help in the GPU department, for example if you tend to run at 90FPS everywhere, you can clamp the FPS in the settings menu to 60 FPS, and the GPU will only work as hard as it needs to in order to generate 60 FPS. This in turn, will lower the heat output, and reduce fan speeds.