Case Fans spin up with GPU

[Deuxez]

So i recently found out that my case fans spin up with the GPU temp. They usually sit around 35% and ive even set it to NEVER go over 35%. BUT they still do. They usually sit around that 35% mark, but as soon as my GPU gets a bit toasty (around 60-75c) and its fans start to spin up (to around 1600-1700) the case fans ALSO do that. I dont know how fast they are going, but you can hear the fans going nuts and the case vibrates for a bit until they are up to "correct" rpm. You can also confirm this by the fact that you can feel the air being moved more. And as soon as the GPU cools down the case fans start to slow down too. 

 

Im using a phanteks universal fan controller connected to my motherboard, with all my case fans connected to the controller (all of them is 3 pin). IDK why they do this!