Originally Posted by
Pob255
If you're still using the original cm690 fans you'll find that the one on the side panel is exactly the same as the rear fan, yet it's louder.
This is not an issue with the fan but the vent in the side panel.
If you use washers or similar to lift the fan off the side panel (ie add about a 3-5mm gap between the fan and side panel) then most of the noise will go away.
Although if you've not added and extra fans to the case then I'd remove the fan from the side panel and put it into rear of the two top fan places instead, as an extraction fan.
That would be of far greater benefit than as a single side panel input fan. (unless you've done some major mod work to the cm690)