If you have an older version of Serato, it may come with the first version of the control vinyl (CV01). There was a manufacturing error with this batch, in that the motor they used when mastering the vinyl was not 'locked' (ie it had unusually high wow/flutter (can't remember which one)). In other words, the vinyl is buggered, and you get pitch drifting. They coded a software fix in later versions (check the setup page and click on 'Drift compensation'). Then there's the new control vinyl CV02 which fixed this problem. So if this is what you mean, then get some new control vinyl, and your problem should be fixed.