On the Imeon 9.12 models, the fan on the bottom right is often the source of the noise. It is this fan that has to be turned on regularly without any obvious need. Tests after manufacture have shown that this fan is not necessary for the thermal regulation of the device. This is why you can remove it from your inverter.
The procedure for removing the fan is attached. Please make sure to follow all steps carefully and to respect the order of the steps.