Hi, I have a G5 twin processor which I bought just before the Intel chip model. It has all sorts of hum and noise in the audio line out when connected to my larger home music system. I have Applecare and the Apple Store tells me that they need to replace the motherboard. I'm awaiting that part to come in now. However, it sounds to me more like old fashioned transformer hum and I'm wondering if anyone else has had this vexing problem -- and if so, how it was finally resolved? I'm too old to keep hauling the heavy unit around much more. Thanks for your time!