I recently installed Mythbuntu and everything is working wonderfully, except that some of the channels come in severely distorted. This first occurred using the listings retrieved from SchedulesDirect. The same thing happened with the same channels when using Myth's internal channel scanner. I've tried finetuning the frequencies, but it never resolves the issue (though sometimes comes close, starting out prefectly clear for a few frames before deteriorating again) and finetuning it to certain frequencies that should give good results instead results in a few seconds of black screen before I'm kicked back out to MythTV's main menu.

I've had MythTV installed on top of other Distros (namely openSuse 10.2) with the exact same tuner and exact same channel lineup and never encountered this problem. If there's any output that would help in diagnosing or solving this problem, let me know.

Check the mythbackend.log, it's normally located here: /var/log/mythtv/. You have to be root to read this file.