Not much gain where it comes to noise reductions, but that could be due to the choice of fans.
you can use resistor-leads or whatcha call them, like these:https://www.aliexpress.com/item/32641234161.html?spm=a2g0o.productlist.0.0.532f4773LmjDda&algo_pvid=43f6e0df-4c9d-49c3-82b3-0c871f39b62d&algo_expid=43f6e0df-4c9d-49c3-82b3-0c871f39b62d-32&btsid=62748aa4-c208-4574-a7b8-7558b4db4a87&ws_ab_test=searchweb0_0,searchweb201602_6,searchweb201603_55
to drop the rpm of the fans.
Thanks. I eventually resorted to using one of these:
Which allows me to change speed as needed.