|Hi, I have encountered similar problem and just managed to solve it.|
Got myself new set of speakers with a better freq. range than my old one. However, there is some noise "Ta ta ta ta .. at times when the harddisk is running"
Finally solve it by taking the power for the speaker from another power point in the house instead of from the multi-socket sharing power to the CPU, monitor... printer... etc.
So try using another power point to remove the noise. Good Luck.