Not sure what the problem is, but, Googling, I see a lot of early problems with the ALC268 chipset in Linux. Here's a link to the datasheet from Realtek:
ftp://207.232.93.28/pc/audio/ALC268_DataSheet_1.3.pdfYou are certain you're using the right driver? I've seen the intel_hda driver somwhere before... oh, yeah. I use it on my Latitude D620. The sound chip for it is a SigmaTel STAC9200. Might want to try something different?
Hope this helped some, anyway.
Later On,
D