I have an iMac G5 PowerPC running OSX 10.4.11. I occasionally use my Mac for audio recording, particularly with BIAS Deck 3.5. I recently discovered noise coming in on my line-in while getting ready to record some audio tracks. I have no audio input devices connected although I am seeing the VU meter pulse when I have the input volume set as little as a hair more than midway in Systems Preferences> Sound> Input. I have disconnected all cables besides the power cable and this still persists. I've tried switching between line-in and the internal mic (which doesn't reproduce the same problem), adjusting the audio MIDI setup and the noise persists. The pulsing on the VU meter in the sound preference isn't steady but somewhat irregular as if there were music or dialogue or some sort of signal playing in the background. Of course this seems to be causing a low level hiss in my audio recording playback (not audible while actually recording). Any suggestions?