I just got some Logitech Z-3's which are much better than my old computer speakers. When I listen to my mp3's at higher volumes, I notice that there appears to be some grainy noise, which I have never noticed with previous speakers, during the vocals. My mp3's are recorded at 128 and 192 kbps. This does not occur with every mp3 file. I also hear grainyness during the windows xp bootup and shutdown sounds (at higher volumes). Is it normal to hear these noises?