I am using my machine to to play CD's and digital files through the headphone output of my iMac to an audio power amplifier, and am getting many incidents of hum and loud pops when the player is not active, and the volume control is all the way down. I have checked and rerouted the cable away from any power source, connected a different amplifier, moved the computer and nothing seems to have a lasting effect. I have noted that the noise often occurs when I open a browser and navigate to a site that may have audio associated with it, or when I open a folder with media files, (not iTunes so far), but it is not limited to those occasions. The noise lasts long after I close the window or folder, and usually quits abruptly, not a slow fade. Has anyone else had a similar problem?