My knoppix 3.3 hd install had resolutions/refresh rates that my monitor just really didn't care for that wouldn't budge when applying the changes in video section of kcontrol. And being female, I could hear the very high pitch of a slightly unhappy monitor before anything was overdriven too long. I felt it was something to do with the ddc probings since I had to modify myXF86Config-4 and literally commented out modelines I felt was not safe long term. It is a newer monitor and it probably would have given me an outofrange if it was set too high but I don't want to overdrive it marginally, either. Oddly, I had no trouble with kanotix and haven't had to edit the modelines or anything other than set a refresh rate I was comfortable with and had a good resulting geometry. Newer version of xfree, maybe?