Michael try a power conditioner or new AC power cord if your getting interface. Then look into DAC (BenchMark or Bel Canto) if the hard drive has USB output. The DAC will improve Flac sound and mps (depending on the source) and the filter will clean-up the source noise.
Audience Adept Response aR1p $495
http://www.audience-av.com/conditioners/ar1p_price.php
BenchMark 1 $1275
http://www.benchmarkmedia.com
Audience Adept Response aR1p $495
http://www.audience-av.com/conditioners/ar1p_price.php
BenchMark 1 $1275
http://www.benchmarkmedia.com