lines appear in movement when using the speed effect.

Hi all,
I desperately need your help! I made a film in final cut pro, and used the speed effect on parts of the film. for example an action done regularly, I needed to make it look in hyper-speed.
The problem is that now I have lines on the screen during the fast parts.
is there ANYTHING I can do?? they appear in FCP as well as when exported. and the speeds vary from 120% to 350% and in all of them, there are lines...
Please help ASAP!!!
Thank you so much!!