stuttering/smirish looking crawl

Hi,
I'm using a MacPro OSX 10.6.8. I'm editing an HD sequence 1440x1080 (16x9).
When I create a crawl across the bottom of the screen it's not smooth, it's very
stuttery/smirish, in other words not clean. Can anyone help?
Thank you,
Dee

you got a screen shot or better yet a clip of the anomaly?

""" What you do with what you have, is more important than what you could do, with what you don't have."

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