Hello, first I have to say that I am not completely sure is was 2000 RPM.
It could have been less, but I'am sure of that I have set a setting in the BIOS that controls the CPU fan (from auto to voltage). And since the RPM is around 800 and vibrations are gone. I'am using the fan which came in the Mugen 1000 box, as you can see in the picture in my second post.
I also took more pictures to show that the cooler is not outlined correctly in relation to the mainboard (it doesn't seem to be aligned with the edge of the board). Thinking maybe I mounted the retention kit wrongly or whatever I have could have done wrong.
Also I didn't dare to tighten the screws on the backplate that much, afraid of braking somthing.
My CPU is a E8500 @ 3.16GHz currently. But was planning tio slightly overclock this to a 3.4 ~ 3.6GHz. Would 800RPM be enough for this?