I have used my Rev.A Bondi-Blue iMac for a good while now solely as a jukebox. It's been doing the same task flawlessly for months, day in, day out - until today. When the power cable is connected to the iMac, the computer (haven't located where abouts the noise is coming from) makes a very high pitched, tinnitus-like noise. Then, when I push the power button in - the noise becomes louder. I tried to record both a video & audio sample but the mic. just won't pick up the sound. There's no startup chime, fans, display. Nothing. Any ideas?