i'm not an expert, but i did have sound problems installing Windows OS in EFI mode.
Did you try booting into the normal CD when installing linux? (If you did it by USB then it probably was EFI mode, since macbooks can only boot that way from them.)
*There's usually two options when booting into CD, when you hold alt/option at startup
Not that i've tried it, but it might be what is causing it.
i'm not an expert, but i did have sound problems installing Windows OS in EFI mode.
Did you try booting into the normal CD when installing linux? (If you did it by USB then it probably was EFI mode, since macbooks can only boot that way from them.)
*There's usually two options when booting into CD, when you hold alt/option at startup
Not that i've tried it, but it might be what is causing it.