This may not help you much, but that buzz you're hearing is just the "sixty-cycle hum". Any speaker will produce this unless you have a noise gate in place between the source and the amp.
Code:
SOURCE --> {PRE|POST} AMP --> OUTPUT
* SOURCE = Computer/guitar/CD player/something that outputs a signal
* AMP = Wherever the SOURCE connects to
* OUTPUT = Speakers
I used to get a
terrible hum from my old tube amp for my guitar - I was even picking up my neighbours' telephone conversations. Then, I got a processor pedal for Christmas, one year, that included a noise gate - no more mosquitoes.
The only thing I can think of is to check each cable and connector in the circuit from your computer to the amp, and then to the speakers.