I received my first Imac replacement today...psu buzz sound here again (even louder i would say, but just when dimming the screen) I looked around the web and this seems to be a common issue. Could it be that the buzzing is actually normal? E.g. my dimlight lamp at home has the same reactions If turned fully bright no sound - if dimmed a buzzing sound occurs. Maybe it's a technical reaction that always happens when an electronical device is working with different currencies. Send back or keep? What is your Opinion?