PVM - Horizontal Bar on SCART

I recently got this PVM which i couldn't tell what model (no sticker at the back). It works perfectly when i connected my wii using component.

But when i connected it using scart (via scart to bnc) to my megadrive or saturn, i got these faint horizontal bar moving up.

Am i missing something ? bad cable ?

Spoiler

 

Hard to tell. I don't recognize the pattern.
But it is some kind of interference, so.. check your grounds maybe?