I have noise from the right and left speakers. Even when the volume is at minimum and no audio cable is connected. It's a bit stronger on the right speaker, or it's almost a whirring sound, not just noise. Is this normal? You can still hear the noise from the right speaker when watching films in quiet scenes. It is less noticeable with the left speaker. In addition, all 3 speakers make a "pop" sound when switched on or off. I have already looked on the internet, there were a few forum posts that had the same problem. There the problem was solved by a replacement unit. But these are all at least 2 years old. Is this behaviour normal? Or is it a DOA case?