That happened to me as well. And I recall I had the problem using the 970's video switching on both S-video and composite.

So I wound up hooking the SMS video out directly into my display and, voila, the problem was gone.
_________________________
Outlaw 970
McCormack DNA-125 (mains), Emotiva LPA-1 (surrounds)
Quad 11L (F&C) Wharfedale (R) LFM1 (Sub) w/ SMS-1
Squeezebox -> Behringer SRC2496 -> Musiland MD10 DAC
Sota Sapphire; Marantz 10B;
Video: Hitachi 42HDS52A; Oppo 971H
System Pics