Not sure if you found resolution.. but consider this...
Your harddrive is JUST lke a record player. Try mounting your harddrive in a vertical position instead of laying it flat like.
Also, perhaps a harddrive with a larger cache over 8mb MIGHT help. I am not sure if the cache is like a DAC with oversampling but it MIGHT solve your problems.
03' Toyota Tundra T3 Special Edition - Polk Audio speakers - Sony 4ch amp - RF Sub amp
Carputer Planning |---------*|
Overall Implementation |---------*-|
Computer installed and working