D300s making noise when above certain power input from panels

As the title suggests, I have just bought an Ep500pro and d300s with 2.4 kw of panels and am getting quite a loud whirring sound being produced above the 500w range of input. Just wondering if this is normal? I want to keep the d300s inside my cabin but this noise is really off putting. Any one know if this is normal behaviour for the unit? Thanks

@RayRay I’m sorry for the inconvenience. It is normal. A single input exceeding 500W will cause this kind of noise.