mac mini noise

My new mac mini (2011 i5 2 months old) Makes intermittent audio buzzing out the analog jack, if I play a sound source or move the volume slider it goes away temporarily and then comes back, as soon as I play a sound source it goes away. If sound output stops for more than a minute or two it starts again. I am using a power conditioner and an audio cable that has transformers that elimoiate ground loop hum. This is clearly an intermittent thing.... This makes it useless as a media player which is what I purchased it for. Its now very noisy in my otherwise peaceful living room, and the only way to fix it is to get this thing working correctly.,

HELP!