I also tried banning the snd-powermac driver and not banning the other drivers and that gave me no sound with an error from Alsa when I tried to run mpg321 etc however when i then did modprobe snd-powermac i got the terrible scratching sound and no music or voice as before. Thus it appears that the snd-powermac module is doing the badness. How can I restore it to sweetness? Thanks Mitchell Laks