CPU Fan Speed - 3 to 4 pin?

Nov 30, 2018
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I've read a lot of questions and answers related to this question on the forum but I never really got the answer I needed. I might be blind at this point because of the long search.
I am currently running a 3 pin CPU cooler, the Hydro Series H100i. They are running at a 100% all the time. I tried to change it through the BIOS setting the CPU fans to DC mode, but the fans are still driving me crazy. It's almost as loud as a vacuum cleaner...
I am open to suggestions for a fix, also don't mind spending a few to buy whatever is needed. I've looked into the fan controllers on different webshops, but my case is closed in the front and it doesn't seem like I am able to install it with this case.

Sorry if I've missed a thread with a question exactly like this.