I have the exact same problem with my R4DS - MP3 playback hiccups about once every 5-10 seconds, when moonshell turns off the screens, and when I drag the windows. Video playback is also compromised. Formated at Fat 16, don't remember the cluster size I set. Kingston 1GB - think it's a Taiwanese one. Running moonshell 1.5 with the 1.05 R4DS firmware. I figured it was a bandwidth issue, as it seems to skip more often when there is more sound in the mp3, a clean vocal didn't seem to skip as often (but still skipped) as a full band playing. I tried encodings from 320kbps to 120 kbps with no noticeable difference in the rate of skip, so then I decided it must not be bandwidth after all - but maybe moonshell's decoding process needs a bit of tuning to work more efficiently on the Slot-1 cards. Hoping that a new version of moonshell will help iron things out. Anyone tried with OGG Vorbis? Any better?