Never noticed that mate. Have you got a dodgy xbox? Are the discs clean? Do you mean that the games are jittery or that you are experiencing slow-down?
Probably just poorly coded/converted games... Ignore if it you can because there's nothing you can do to stop it
It can also be due to when the xbox is chucking a lot of stuff around in its memory: you can get lags when the ram can't keep up with the cpu. depending on your spec, pcs suffer from this so this is what you might be seeing. Some games that use the xbox harddrive (like morrowind and halo) "glitch" or stutter when they're loading -- better this than load from dvd. It's as close to seamless as you're going to get. Vice City just suffers from slowdown. Try driving the tank in GTAIII and see what I mean. regards, anephric
Might also be due to your frame rate settings on the dashboard. Some games run better in 50hz eg Halo (runs very jerky in 60hz). Try playing them in the different modes.
I don't have the games you say are juddering, but I have never had this problem with any of the games I own or have played on my Xbox... Regards, Iain.
Are you using the naff cable that came with the xbox or have you changed to the Advanced Scart, could help, and even if it doesn't your still gonna get a much better picture.