SNES Mini is modded for RGB, i'm thinking maybe it's an incompatibility between the cable and the mod on the SNES? At something of a loss...
EDIT: Additional info! Hookep the SNES Mini up to my Vigatec FX2. Here's the results:
SNES Mini with PAL SCART cable (Just tried it for the hell of it).

SNES Mini with US SCART cable.

As you can see the picture of the SNES with the US SCART cable is really washed out, no detail in the backgrounds (until the screen fades) and generally just very off.
Here's a video showing what's happening: http://www.youtube.com/watch?v=OXP1sY06 ... e=youtu.be
Also, the top 1/5th of the screen is unaligned with the rest of the image and vibrating very quickly. Tried to capture it here: http://www.youtube.com/watch?v=ySotCXlN ... e=youtu.be
Any help with ironing out these issues would be much apprecited, particularly getting this working on my CRT.