That is the case with my F6 Pro. It happens usually when power consumption is low i.e. CPU at idle/Package down to C3 or even C8. There is no way of avoiding this issue and most laptops will have it. Sometimes even high end premium expensive laptops have this issue, such as the XPS series.
There is no reason to be concerned; most of the laptops I have worked with have some sort of coil whine, though I agree, the F6 Pro’s whine seems to be excessive.
But uthen again, what did you expect from such a cheap, yet premium feeling device with great battery life? They had to cut corners somewhere.