Yep...strange sound from the side panel when it is mounted.
In my 800D also hear it.
The panel acts as a membrane, enhances the vibration generated by the pump.

cstkl1 use push-pull for slow fan speeds.
Capacity will increase slightly but do not expect too much.
I was not enough so I chose a very effective solution.
I plan to add Black Ice SR1 560.
Work in progress...